Edit animations in existing games?

Sorry for the complete newbie question. I’ve asked around everywhere to no avail so I’m trying here.
I don’t know if it sounds ridiculous but is it possible to use UE to edit the animations in existing games like Borderlands for example?
All I want to do is straight up remove death animations so that deaths are pure ragdoll (the game already has ragdolls) and all I’ve been told is I’d need “extra software” to do it but not which software I’d actually need.
I haven’t got the slightest clue how I’d go about it, hence me asking on here. I just wanna be pointed in the right direction as I’m happy to learn how to do it myself.