You can switch back and forth with some effort but it will slow learning of the new layout. I think you're on the right track with using different keyboards though. Ideally they should be very different with different switches, keycap profiles, etc. I use QWERTY on a RF Topre board at work and Colemak on Cherry Blues/Macbook scissors at home. I find that I can switch effortlessly between the two because the typing environment is much different.
If I switch the layout of my Macbook to QWERTY it takes some effort to remember which layout I'm on. It took me about 6 months to a year of typing on both layouts to be able to switch on demand. I still have certain hurdles that are very difficult to overcome. For example, I normally use Unix shells on QWERTY. Using a Colemak at the command line requires a lot of focus. Typing emails, is trivial on either.