Player model and hitbox .

     Hello there ! 

So as I am doing a fallout minecraft mod I did one of the most emblematic elements of the game serie which is the FEV , which allow to turn creatures into mutant , I managed to make it possible for npc by a simple trick , if an entity dies into the FEV and that it is a "human" character it spawns a super mutant but now I want to make it possible for player to become themselve super mutants but I'm standing in face of a massive problem now , since I don't wan't it to look silly by just giving effects to the player I'm wanting to change both they're model and they're hit box , and of course to make sure that it will only affect the player who diped imself into the FEV and not all the players in the world .

If anyone knows how to do so I would be so thanksfull if you give me a little help !

See you soon fellow modders !