All questions regarding mapmaking for Heroes of Might and Magic 3: The Shadow of Death.

Using standard game mechanics, it's probably impossible to make a single cell trigger an event multiple times. Unless you make the event non-cancelable after the first visit. You could fight as many times as you want, but besides experience, it wouldn't give anything else. This isn't a good option if this cell is on a path and will be visited multiple times. But if you really need to do it differently... You could place several events on a single-cell road leading to some object, each event for a "specific" player. Or, you could have several identical objects, and before each one, place a guard that requires the player to be of a certain color. And behind the guards, place the events.