I don't think that's quite what he meant.
If I understand it, he wants to have different enemies in different parts of the same map. Like in most RPGs on the world map, you can go to different continents where there are different enemies to another continent. Setting the enemies in the properties will make those enemies appear in all areas of the map.
I don't think it's possible in XP, but that's only from looking at it quickly. In VX you can easily do this with the "New Area" option, but XP is lacking that.
Try looking for a script that does this. If not, I can probably write one up for you that should do what you want it to, though it won't get started until after Christmas.