Have you ever wanted to have example resourcepack for custommodeldata tag? Here it is! If you dont know what is custommodeldata, basically it makes "another id" for any item and you can change texture for specifically this id instead of item itself

this resourcepack changes iron ingot with custommodeldata:
556 - gold ingot
557 - diamond
558 - dirt

to give yourself item with custommodeldata tag use this command:
/give @p iron_ingot{CustomModelData:556}

check iron_ingot.json for more information how this works

p.s. sorry for bad english :3