Replacing Character Model with NPC model ?

[LeMao143]

Hello, I am super noob with mods and I'm trying to replace Trevor's model with that of an NPC, particularly the Groom "ig_groom.ydd" is his file name.

I know I can just use the Character Menu mod and just play as him but I wanna be able to retain the character model through missions and stuff.

Please let me know how I could do this, thanks so much!!