Like creek_devil said, the short answer is "yes", you can do it if you're using a floor controller with switches, or even with a stand-alone latching switch (like the Boss FS-5L shown here:
http://www.music123.com/Boss-FS-5L-Foot ... 5.Music123)
The way you do it is assign a modifier to each of the two amp blocks (I would tend to assign it to the "level" parameter). Set the modifier for one amp to be one way (0% when switch is off, 100% or whatever level you want when the switch is on), and set it the opposite way for the other amp block (100% or whatever level you want when switch is off, 0% when the switch is on). In both cases, simply assign the same controller (or pedal, if you're using a standalone like the Boss unit) to both modifiers. Bingo, you're done.
Incidentally, it's exactly the same process to assign a continuous controller to morph between the two amp blocks, except you also have to play around with the curves of the modifiers (using the middle value, as well as other parameters such as slope), to get a smooth blend in all pedal positions. It's simpler with a simple toggle switch (like what you're currently looking for), because the middle position and anywhere in between doesn't matter at all.
Daniel