To those who still are wondering how to convert an additive animation exported from umodel back into a "FULL" animation, I did a video on it.
However sometimes you need to do a bit more to fix the anims (sometimes the bones location are off), and Bmbr gave me some instructions on that where he fixed it for Gears 1 but I could not figure it out.....
"all i did was to apply the anim pose for every keyframe
so you had with the animset those 1 frame idle anims
i had jus copied that pose and then press I and choose location
and you need to apply correct pose for every anim"
"i think it can be done via editor
cause when you sent me the fixed offsetz anims
i didnt had to put all poses to each keyframe"