Download
Run
Enable shell functions
Right click a map file
Choose "Edit Scenario"
Change as you wish
Click save
Also copies the new scenario to the clipboard, so you can simply paste it to your mainmenu.

Edit: Credits:
KKC - Finding a small bug that I racked my brain on for two hours before realizing how easy it was to fix.
Anthony - Some registry help on the first version.
Trep - Who's render I used for the icon.