Game stores particles in .pcf files, which are located in reactivedrop/pak01_dir.vpk and are in the directory reactivedrop/particles. One .pcf file contains many particles. For example, fire_fx.pcf has particles for flamer and vindicator nade.

Before the latest update we couldn't add custom .pcf files, because overriding particles_manifest.txt was forbidden (particles_manifest.txt makes your game read .pcf files. You couldn't upload to workshop, but you still could place your .vpk's in reactivedrop/addons and it would work). So modders had no other way of replacing particles other than replacing the whole .pcf file at a time.

That is an issue, because addons that replace particles which are in the same .pcf file would conflict with each other. For example, if you are subscribed to an addon which replaces vindicator grenade particles and also subscribed to an addon which replaces flamer particles, they would conflict and only one of them would work.

Let's say you want to change the color of flamer to red. You need to extract the .pcf files using GCFScape which are located in Alien Swarm: Reactive Drop/reactivedrop in pak01_dir.vpk. The directory is root/particles.












After saving them somewhere, you will have to find which one of the .pcf files contains the particles you want to replace. To search them, you need to install Alien Swarm: Reactive Drop - SDK. After installing it, launch it and select Reactive Drop (Tools Mode). On the top bar, click Tools > Particle Editor. Then, do File > Open and select a .pcf to see which particles it contains.








For example, flamer particles are in fire_fx.pcf.

Once you have found which .pcf file contains the particles you want to replace/change, copy and paste the .pcf file, then rename it to something else. Then, in the particle editor, delete all other particles in that .pcf file that you don't want to replace/change, so that the .pcf contains only the particles that you are modifying. In this guide I won't be showing how to modify particles, there are many tutorials on the internet on that matter.
Sidenote: don't rename your .pcf to something basic like a.pcf, ideally we don't want addons which add .pcf's with same name, because they would conflict as well. In my case I have a jh_myredflamer.pcf with only 5 particles that are getting replaced.

Also note: do not change particle names, because game uses particles based on their name.

Now that you have your custom .pcf file, you need to pack it into .vpk and put it in a correct directory. .pcf files are located in root/particles, so we will be using that directory. Create a folder on your desktop (name of the folder doesn't matter). Then, in that folder, create another folder called particles. And inside the particles folder is where you put your new .pcf file.

Also you will need to put a particles_manifest.txt into that particles folder, that way you show the game to read the particles inside your .pcf. Particles manifest should look like this (Obviously instead of jh_myredflamer put your own .pcf name).
You should end up with a folder which looks like this:
To turn this folder into .vpk, you need to drag it onto vpk.exe, which is located in Alien Swarm: Reactive Drop/bin. Best way is creating a shortcut for vpk.exe and keeping it somewhere for future addons. So just take your folder and drag it onto vpk.exe shortcut.
This creates a .vpk which is ready for you to upload to workshop (At the time of writing this guide you can only upload addons which modify particles_manifest.txt in the beta branch). But first you should always test if it works, you just put the .vpk into reactivedrop/addons folder and launch the game.

That should be all. This way your addon replaces only specific particles and not all the particles in a certain .pcf file. Here's the result: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2083443961 Feel free to unpack it and check for yourself how it was made. If you have any questions, ask them in the comments.