That is already the simplest method.Also its just unpack your sr3 character files and rename every file of that pack with the name of the sr4 character files you picked for the sr3 chars.got a simpler method? or could you give it a try, I'm not good at working with 3d models.
But he didn't offer to edit the lua so no its not what he said above.Also the question if there is a more simple method wasn' answered.This is what Henry said 2 post above.
just unpack your sr3 character files and rename every file of that pack with the name of the sr4 character files you picked for the sr3 chars.
It's kinda easy, you should unpack SR3 arhive with the character rename files here to match some other character in SR4
repack the files store them in the sr4 root folder and run minimauls update tool to actualize the asm_pc files that's all.
pack them to SR4 acrhive, put this arhive and characters.asm_pc file to SR4 folder and update asm.
Yeah,my bad that was another thread but i found to go a little more in detail and telling that the files inside of the archive have to be renamed too could help if someone is new to sr4 modding.You didn't offer to edit lua too lol