If the beans are from your pantry, then the frozen corn will thaw quickly and make the salad cold
and good to eat almost instantly!
Swap other types of tomatoes or salsa for plum tomatoes. If you use salsa, mix a tiny bit with the vinegar separately first to make sure the flavors mix in a way you like. I would not suggest canned tomatoes.
I've used red, white, or yellow onion, depending on what I have.