Ah, I forgot that UTM grids are disabled on the color aerials. It's because they are in a different projection, but I can make a note to look at adding them.
To answer your question about musical USB sticks -- what you are describing is possible right now, but perhaps a little cumbersome. The calibration info for each map is saved in the TopoFusion.ini file, so you'd need to copy that over too.
However, if it's of use to you and your team, I have been meaning to add a calibration export function that would make this process easier. You'd just need to store the original image and the calibration file on the USB to be read by the copy of TopoFusion on the laptop.
By the way, the user maps are not stored in the mapsX.dat files. They are loaded from wherever in the program you initially load them from. We'd make it so when you add a new image it looks for an appropriately named calibration file and loads that, if it exists.
Does that make sense? Let me know how we can help you.