Modifying existing animations?

To be honest, you've already figured out quite a lot for a beginner. Good luck, and I wish you further success. Keep us updated; you might find something that we don't know.

Added 7 minutes later
I'll try to write something constructive about your task later; unfortunately, I don't have time right now.

I tried to create a new animation and add it. I followed the guide of a great guy, Esto100nec - https://www.youtube.com/watch?v=uDgiUL8kdbg

I learned two things:
1. Don't try to put the animation into data.pak. The game stops launching, and only reloading the entire data.pak fixes it. Deleting the file that was put there doesn't help.
2. Adding new animations doesn't work, apparently. I wrote everything correctly in the configs, but the animation didn't work. It seems that only replacing animations works. I might be wrong, as Esto100nec didn't show how to import animations back into the game. I asked him about importing, and I'm waiting for his answer.