You're right, I forgot about that. It is for enemies chance to hit you. So then there's no way to make it so that XCOM has a higher chance to miss after hitting, unless someone comes up with a mod for that.

Sadly "hit streak" is purely for the enemy. It's another help for the player if the AI hits you too often.
When the AI constantly hits (hit streak) they get -5 for each consecutive hit (if you set Hit-Streak Hit Chance Adjustment to -5). But the player isn't affected by this mechanic. You can hit as often as you want without any aim debuff.
The description is "Reduced hit chance for aliens after consecutive hits." aliens, not xcom. Sad, but thanks for the linked thread :) It's generally very insightful.

Yes that is definitely possible. This reddit post covers how to change the "AimAssist" settings.

https://www.reddit.com/r/XCOM2/comments/45u81x/yes_xcom_2s_rng_cheats_in_your_favor_heres_how/

Set the "Hit Streak" for -5 (so each shot after a hit has -5 and stacking until you miss) and "miss streak" to 5 (so each miss adds +5 until you hit). Keep in mind if you change the settings yourself AND subscribe to this mod, you may get mixed results. Just do 1 or the other (change the default settings yourself, or use this mod and only modify this mod's settings).

Hey, not sure if you still read this stuff or know how it all works, but i have a question to the following.
You wrote "In a few situations, it also has the opposite effect of reducing your chances when you have a string of successes.". Where can i find this please?? I would love to have a +5 buff for every consecutive miss, and a -5 for every consecutive hit. I hate it both when i constantly miss 80+% shots (missed 5 shots in a row that were around 88%...), but i also don't enjoy hitting 5 or 6 50% shots in a row. Both instances make the game either too frustrating or boringly easy.

Today I Learned. Thanks, definitely gonna be using this mod.