I hate to get one up on the guru, but providing the version does not have a different pulse engine, and most dont, you can have multiple versions of Mach3 installed. Just make sure you install it to a different directory, and not use the dektop shortcuts to open it.
You will need to open Mach from within the actual folder, or create and label new shortcuts.
Remember this is dependant that the pulse engine has not also been updated.
Yell me down, I am happy to be wrong