Currently.... Aside from renameing another map#.mul file, and coding it to be readable to the clients, there is another way to do this.
You need a couple things, First, an EMU that supports MapDiff.mul and the others (statics/staidx) And a tool (will re-post where you can find this tool soon) that allows you to modify the Diff files.
Basicly, you would copy one of the maps into the MapDiff files, and you have 2 working worlds/facets.
We did this, Using our custom map as the Felucca Facet, and Tramell (yes, haven and all) as.. well, the Tramell facet. Still giving use to the Map2.muls, to eeither Modify, Or leave as Ilishnar.
Although we are not intending to use them like this, It was a test to see just how much the Map/Statics/Staidx -Diff- Files could hold.
And we found that they will indeed hold an entire map, ie, Map0.mul.
Just one of a couple ways to do what you ask.. So, the answer is, Yes you can
