Here I shall list all of the changes and features I’ve implemented in this mod, as well as try to explain how these base changes effect gameplay and, whenever possible, advise players how their strategies should change when approaching religion when using this mod.

One thing I should like to note is this mod is more aimed at tweaking the vanilla game rather than completely overhauling the EU4 system—as is done in mods like ET and MEIOU and Taxes—to keep this mod as cross mod compatible and easy to update as possible.

If you want to skip the detailed explanation, at the bottom of this post you can an itemized list. (Coming soon)

Major Changes:

I. Religious Conversions are More Difficult – Over the years I’ve found that it’s become trivially easy in Eu4 to mass convert heretic and heathen provinces, and that there are so many sources of easy missionary strength that there is rarely a need to pick up the Religious Ideas unless one wants the Casus Belli it provides—and further both the player and AI face little challenge in conquering vast swaths of territory from alien religions since you can change entire regions which have remained historically resistant to religious coercion for hundreds of years and sometimes over a millennia. The first manner in which I address this is to dramatically reduce the initial missionary strength all tags receive, so as to make the later bonuses one gets more important.

Originally the base Missionary Strength Bonus for all was +2%. Now it is 0% against Heretics, and -2% against Heathens. Meaning you will have to purposely invest in your clergy, advisors, ideas, etc. if you plan on converting a good deal of provinces, especially if they are non-pagan heathens. It is advisable if your general path of expansion will include a good deal of provinces of other religions that you choose either the Religious or Humanist ideas.

However, if the player (or AI) finds themselves in a position where they have low religious unity and no conventional way to deal with it in the short term they may now take the decision to "Declare Religious Ban", which simulates the various times throughout history that nations dealing with significant populations of religious dissenters enacted restrictions and penalties against adherents of these faiths to ensure the stability of the state religion--for examples the edicts against Christians during the former Roman Empire, the poll taxes employed by Muslim states during the middle ages, the anti-Catholic Penal Laws of Great Britain, etc..
Declaring a Religious Ban applies a permanent (unless disabled) modifier to the country:
+25% Religious Unity
+1 Tolerance of True Faith
+1 Global Unrest (penalty)
+25% institution spread in true faith provinces
-25% institution spread in all provinces (penalty)
+10% Tax efficiency
-10% Production efficiency (penalty)
-10% Total Manpower (penalty)
You can only remove this modifier after 10 years, at which point you can take a decision, at the cost of 50 Administration points, to "Repeal Religious Ban". (The Religious Ban Decision may be taken an unlimited number of times as the player sees fit.) As you can see from the modifiers above a Religious Ban will significantly increase your Religious Unity, at the cost of some unrest and slowing of institution spread in your heretic and heathen provinces, however the bonuses will mean your true faith provinces remain the same as before. While the ban is in place you will receive a slight penalty to manpower and production efficiency, but a slight bonus to tax efficiency, to simulate the such Bans often increased tax revenue at the disadvantage of discouraging disbeliever participation in military and other national labor.

(The AI has an additional increased penalty to missionary strength, but also a slight bonus to heathen/heretic tolerance and reduced missionary cost to compensate, as I’ve noted the AI is not very good at dealing with non-“True Religion” provinces other than to mass convert them. Expelling minorities has also been disabled for the AI, to prevent them from abusing it. Spain will no longer mass deport the population of Southern Italy to America.)

II. Certain Areas and Cultures will be harder to Convert – Generally speaking most of the already Established religions within the game have cultures in which they are stronger and thus harder to convert, through a cultural penalty to local conversion strength (Similar to Muslims in the vanilla Game). This varies between 1% and 2%, depending on the innate conversion penalty of their preferred religion, thus traditional Muslim and Coptic cultures receive 1% while Orthodox and Catholic stalwarts receive 2%. In addition to this, all the new religions (Protestant, Sikh, etc.) which appear during the game receive an innate boost to de-conversion through penalty to local conversion strength, to make them harder to stomp out, though this is balanced by the fact that the cultures they are easiest to spread to lack an innate conversion penalty. (See full list at bottom.)

III. Overhauled Protestant Reformation – the Protestant Reformation worked somewhat well when the game first released, though still fairly distant from historical reality; and over many subsequent patches and Expansions it has become something of a mess—too often fizzling out without active player intervention, yet even if the Protestant faith gains a foot hold the Reformed faith rarely manages to survive. All of that besides, the game rarely managed to produce many of the interesting situations which actually emerged during the period, like the struggles of the Huguenot Calvinists in South France, the Puritan Revolution in Great Britain, or the emergence of Unitarianism in Transylvania. Thus I have greatly reprogramed the manner in which the Protestant Reformation fires and spreads to both more dynamic and historically accurate.

Let me first note that I’ve changed the rates, number, and appearance of Centers of Reformation. Protestantism, which can emerge in the North German region, spreads slowly but gains momentum as more countries convert to the faith: Protestant Reform Centers convert at a rate of 2% but there can be as many as 7 centers in Europe. The Reformed Centers, which can emerge in either the North or South German region, converts much more rapidly (5%), but can only have two Reform Centers at a time. However, to account for the fact that the Reformed faith, both in terms of gameplay and history, often grew in areas under regimes that did not recognize their religious freedom, Reformed Centers do not require the conversion of a tag to spawn; so long as there is a single center of the Protestant Reformation (the success of both faiths are tied together) and a single Reformed province, there is a high change a Center of Reformation will spawn there by event—the likelyhood of this event firing increases if the owner is Reformed. Further, both the Reformed and Protestant Centers will prioritize their targets based upon their culture (see full list below), and the Protestant Centers will leave certain cultures for the Reformed faith to spread to alone. Further, certain cultures these Centers will outrights avoid—like Italian and Polish, again see full list below.

Lastly there is Anglicanism, which I have made several significant changes to (and soon more to come), but let me begin with their Centers of Reformation. Anglican Centers still have 5% strength, but there can only be one at a time, and they can only appear in the British Isles. They will spawn in the Capital of the first Anglican Nation, usually England/Britain, and only if that capital is the Primary culture of the owner; if the capital changes, is no longer the primary culture of the owner, or the owner is no longer Anglican—that is the owner converts or the capital is annexed by another nation—then the Center will disappear, however a new Center will spawn in the new capital of that Anglican nation, or any other. Further, the Anglican Center will only convert provinces of the owner’s primary culture, and within the British Isles. For example an Anglican Center in England will only convert English provinces in the British Isles, but not Scottish in the British Isles, or (hypothetically) English provinces in continental Europe—however the player can manually convert any provinces normally.

Note: a large portion of British Isles will remain occupied by non-Anglican religions--so it will likely be advisable to Declare a Religious Ban (see section I.) until the Reformation ends. Firstly the Reformed faith will spread to Scotland as well as certain areas of England, and in some cases will even convert Anglican provinces if they are of the correct culture and area. These provinces can of course be converted back to Anglicanism, but keep in mind that until the Reformation ends you have to deal with a large Reformed population—there are plans to update this mod with more Anglican Religious Actions that will allow the player to interact with the Church of Scotland, English Puritans, and Irish Catholics that will grant miscellaneous additional bonuses and help boost religious unity further. Secondly, during most normal conditions Ireland will remain largely Catholic through a feature I will explain next, historical Catholic cultures.

There is a high likelihood that provinces of certain cultures, like Irish or Polish, will spontaneously “Reject the Reformation” should they be converted to a “Reformation” faith, regardless of the owner. Thus, should a non-Catholic Christian player (with the exception of Orthodox and Copt) come to own a province of any of the historical Catholic cultures (listed at the bottom of the document), then they had better plan on dealing with a near-permanent heretic province. This event will fire so long as the Papal States exist and are not the vassal of a non-Catholic nation—thus if the player wishes to see, for instance, a Protestant Spain, then they need to ensure that the Papal States are either destroyed, or are their Vassal.


Full list of Changes:

Universal Base Missionary Strength –
Vs Heretics 0%
Vs Heathens -2%

Changes to Denomination Bonuses –
Protestant: -2% Local missionary strength penalty
Reformed: -2% Local missionary strength penalty
Anglican: -1% Local missionary strength penalty
Sikh: -2% Local missionary strength penalty
Jewish: -4% Local missionary strength penalty

Cultural Penalties to Local missionary strength –
Celtic:
Irish: -2%

French:
Francien: -2%
Burgundian: -2%
Norman: -2%
Breton: -2%
Wallon: -2%
Aquitanian: -2%

Iberian:
Castilian : -2%
Leonese: -2%
Galacian : -2%
Portuguese: -2%
Basque: -2%
Aragonese: -2%
Catalan: -2%

Latin:
Piedmontese: -2%
Sardinian: -2%
Ligurian: -2%
Lombard: -2%
Venetian: -2%
Romagnan: -2%
Tuscan: -2%
Umbrian: -2%
Neapolitan: -2%
Sicilian: -2%
Maltese: -2%

German:
Austrian: -2%

West Slavic:
Polish: -2%

South Slavic:
Croatian : -2%
Serbian: -2%
Bulgarian: -2%

East Slavic:
Byelorussian: -2%
Karelian: -2%
Muscovite: -2%
Novgorodian: -2%
Ruthenian: -2%
Ryazanian:-2%

Byzantine:
Greek: -2%
Gothic: -2%
Pontic: -2%

Baltic:
Lithuanian: -2%

Caucasian:
Armenian: -1%
Circassian: -2%
Dagestani: -1%
Georgian: -2%

Carpathian:
Romanian: -2%

Cushite:
Amhara: -1%
Sidamo: -1%
Tigray: -1%
Afar: -1%
Oromo: -1%
Harari: -1%
Somali: -1%

Sudanese:
Nubian -1%

Maghrebi: -2%

Arab-Turkish:
Turkish: -1%
Egyptian: -1%
Syrian: -1%
Mashriqi: -1%
Gulf Arab: -1%
Bedouin: -1%
Mahri: -1%
Hedjazi: -1%
Yemeni: -1%
Omani: -1%

Iranian:
Persian: -1%
Baluchi: -1%
Afghan: -1%
Khorasani: -1%
Luri: -1%
Kurdish: -1%
Azerbaliani: -1%
Mazandarani: -1%

Tibetan: -2%

Altaic:
Mongol: -2%
Chahar: -2%
Khalkha: -2%
Oirats: -2%
Uzbehk: -1%
Turkmeni: -1%
Uyghur: -2%
Khazak: -1%
Kirgiz: -1%

South-East Asian:-2%

Chinese: -2%
Korean: -2%

Evenki:
Manchu: -2%

Burman: -2%
Central Indian: -2%

Eastern Aryan:
Sinhalese: -2%
Oriya: -2%
Pahari: -2%
Nepali: -2%
Bihari: -2%
Kochi: -2%
Assamese: -2%

Western Aryan:
Marathi: -2%
Malvi: -2%
Gujarati: -2%
Rajasthani: -2%
Saurashtri: -2%

Hinsustani:
Hindavi: -2%
Avadhi: -2%
Vindhyan: -2%

Dravidian: -2%

Reformation Center Preferences –
Protestant: Saxon, Westphalian, Pomeranian, Prussian, Danish, Swedish, Norwegian, Czech, Silesian, Slovak, Estonian, Latvian.
Anglican: British Isles and Primary culture of Owner.
Reformed: Scottish, Highlander, Swiss, Gascon, Occitan, Basque, Swiss, Dutch, Hungarian, and Transylvanian. Areas of Loire, Poitou, East Anglia, and East Midlands.

Historical Catholic Cultures (will sometimes spontaneously reject Reformation, see section III) –
Irish, Castilian, Leonese, Aragonese, Catalan, Andalusian, Portuguese, Lombard, Tuscan, Sardinian, Piedmontese, Romagnan, Ligurian, Venetian, Neapolitan, Umbrian, Sicilian, Maltese, Polish, Croatian, Lithuanian, Burgundian, Wallonian, Norman, Breton. Also Francien if France is Catholic