It works on other maps too, if you have a mod with a custom map, just load it after hardcore desert in modsconfig.xml, I think I tried that before and it worked.
Or unpack HardcoreDesert.mpk and change the map file in content/map, then repack it using 7zip or winrar, it a zip with no compression, then change .zip to .mpk
If you want the king on a custom location you have to create a final boss zone in your map using the editor and hardcoredesert.mpk, if you don't have this zone, the king will spawn in normal boss areas.
Also if you want to complete the last quest with the teleporter, you need a snow alien zone.
if you change the map, I suggest you keep some savegames of your progress just in case.