I don't do a lot of customs, but I remember taking that tiny screw out the first time I repaired an O-ring. When I was younger I would change pants when someone had an accident and joined the BCB (Broken Crotch Brigade).
Lost thumbs would only bother me when they were a favorite, and they didn't happen that often. As long as they had one thumb, they could hold a weapon and the "damaged" hand could be posed toward holding the clip.
I swap out heads and switch parts around, mostly to give current characters a wardrobe update, but occasionally to create a new character. I'm not too much into painting/dremeling.
Although I did do a badly wounded soldier that I will post some day. He's a mess though, probably would rate him PG-13. I feel disturbed when I see him.