Correct, you have your base map, and then there is the auxiliary maps... that are offsets of the main map.
Example - at 4000rpm, 10psi of boost lets say your map says 8ms of fuel. The aux map has just as many cells as the main map (32x32 grid) so at that same point, you can add or subtract fuel in ms of fuel. Same thing with timing, 23 degrees, then plus or minus whatever you want.
So, basically you do have map switching ability.