[Replace an NPC with another race?]

I now have a custom race in Creation Kit. I finally figured out that, to replace the NPC(s), I just go into the CK, find their race, and edit their skeleton and texture. Sure, I did it with a piano, so it just floats around, but I did what I wanted! I'M HAPPY!!!

[I would like to replace the male child model with a piano. How do I do that?]

I'm new to modding. I'd just like to replace the male child model with a piano that I made. The best I've found is how to replace an inanimate object, for which I ran into an error of "Could not insert NiBlock; unknown block" in NifSkope while trying to paste something from my piano.nif (also made myself) into the maleChild's directory.

[Replace character model with custom model?]

I would like to replace any given player character model in GTA V with my own character that I made in Blender, but I don't know what I need or what to do. So, how do I replace let's say Franklin's model with my own? I probably need the skeleton, but where would I get that?

[GOG Witcher 3 can't find with NMM]

I'm running it on .65 update and I'm having the same problem. I think it's because of GOG Galaxy screwing things up because NMM refuses to work with the main game files. Do I have to move the whole folder to somewhere else or am I just out of luck?