It is possible to have more than one copy of Awasu installed at the same time (although you cannot run more than one copy simultaneously). It is best to install additional copies of Awasu by unpacking ZIP files rather than running the installer, to avoid confusing the installer as to where Awasu is installed.
The main issue is that Awasu stores your data files in the Windows user directory (e.g. C:\Documents and Settings\YOUR-NAME\) and so would normally be accessed by each installation of Awasu you have, not good if they are different versions.
To avoid this, you should run each copy of Awasu in portable mode or otherwise force them to have their own set of data files.
GUI settings are stored in the Registry and are not backwards compatible. This means that if you are running two copies of Awasu that use different versions of the third-party GUI toolkit we use, when you go back to the older version, it may well crash on startup (as it tries to read the Registry settings saved in the newer format).
To work around this, you can either run ResetUi.exe to clear the Registry settings or create a DEBUG.INI file in your user's local data directory to force each copy of Awasu to store its settings in a different part of the Registry:
RegistryKey = XXX