I'm not real sure but I don't think it would work cause tomato's are aggressive anyways
A maroon clown and a tomato clown are not the same. Maroons are much more aggressive.
To answer your question, ,if I were you, I would stick with just the maroon now, or else, take it back for store credit. The maroon is pretty good size, which means it will probably be pretty aggressive. You may haave been able to pull it off if the maroon was really small. The other option is, of course, get the other fish and see what happens. The tank is decent sized and if there is a good bit of rockwork, it may be ok.