I'm making an underwater city. When I will be finished I would like to have citizens and guards in it. Is there a way I can either make an entire new entity or just edit a Villager's skin and get rid of trading. For the guards I thought I can change the skin. Or is there a way I can make them kill anything else within its radius except for myself and a few other players as well as the citizens?
There is no way to make a villager attack another mob without rewriting code within the game files, which isn't gonna happen. The best you are able to do is to summon iron golems with
/summon VillagerGolem ~ ~ ~ (The capitals are necessary)