I have always modified the .mnu, but I always have it backed up just in case. The problem with edititng the .mns is that if you reload the mnu and the changes are not in there, the mns will get over written with the mnu and all your changes will be lost. Another way is, when you make the changes to the mns and test them, if everything goes a planned delete the mnu rename the mns to mnu and reload it.