Without "bovirus" explaining his reasons for wanting to change the mapset info it is had to see without an example of what map or maps he is talking about.

I for one do not spend any time on my maps with the GPSMAP 66 other then turning on one map and turning off the other.
The rest of the time is with the map screen as I Hike or Bike.
Same with my SmartDrive 66. I turn it on and plug in where I want to go and drive.
The mapset info plays no roll as to how I use the GPS.
I spend most of my time working out what paths I will take in a GPX file or files when I take a group hiking or when I am on vacation.

This is all done in Mapsource with the same maps I have on all my GPS's then just copied the completed GPX to the GPS

PS:
I know of all this programs at Javawa along with many other tools I have.

The one program I use all the time is JaVaWa GMTK.

After installing my maps to the Laptop I use this tool to move them to my portable Hard Drive and free up my Laptop.

At the moment I have close to 50GB's of maps that I use in Mapsource.
The JaVaWa GMTK does a very good job of moving installed maps to another location.