Once again, Sonic has the answer, but be careful since I do not know of anyway to export/import a subset of units, such as heros. I wanted to do this awhile back and could not find a way to do it. So, if you have some units that you want in each map, you can't export/import without overwriting the units in the map you import into. The best alternative I found was to open both maps and copy/paste between them, but on my systems, the WE is slow to toggle between maps. It took about 1 hour to copy 50 units.
Eric