How to replace players bodyparts with custom models using a script

Hello! im working on a gore-shooter game, and i got my own pretty bloody arm model, i want to make it so when the player shoots another player in the right or left arm, it replaces the left/right arm with my custom model, the problem is that i can do that but idk how to make it so the custom model acts like its the default arm, i already got a shooting system that detects which part was shot, i just need help with replacing the model and making it works, please help! thanks

Just make the body parts invisible and weld the gore body parts onto the original (invisible) bodypart.