Easiest thing to do this would be to remove registry keys by diablo 2, then you just install diablo 2 again but in different folder, that way you will keep your MXL and you will also have diablo 2.
Not at home right now, so I can't post any screenshot, but was able to find sth.
Run registry/regedit, google it if you need and delete the marked folder/s (Diablo II only), you can also right click on it first and export it to somewhere, just in case:
