Custom textures help (for survival <3)

Hee! Me and my friends are making a survival server and we want to be able to get custom items. I want people to be able to change already existing items (For example you have a stack of golden carrots, and want to change that into pizza for free.) You're able to do that using "Custom Roleplay Data" datapack, and the command: "/trigger CustomModelData set [num]" However i just can't figure out the scripts in the resourcepack myself.
Ive managed to make the vanilla way work, but only using /give.
Could i get help fixing my resourcepack, a proper example resourcepack, or something else that you think helps me better?