Andy - This is possible, but recommended only if there is no other option....you must be careful not to become confused with two installations. If you install one version to all accounts, and the other only to one account on your machine, then both versions will work.

If you do this, make sure the launch icons and other aspects of both installations are clear to help you distinguish which installation is launching? vs which is updating?

We don't recommend typical users to do this because it can cause confusion. For example, we speak to a client on the phone and ask them to install version X. They then mistakenly start version Y, because they have two installed. We spend hours diagnosing a problem that doesn't exist.