The recommended practice is to choose a virtual drive assignment and stick to it; commonly, this is drive Q: - so what happens if you want to change to something else, for example, V:
If all applications were equal and followed recommended practice, then simply changing the environment variable %SFT_MNT% on the client would enable you to change the virtual drive at will and no applications would need to be re-sequenced; however, not all applications are equal and this can cause some issues.
Some applications hard code the installation drive in the registry or configuration (INI) files - This means you have several options:-
As with all applications, if you decide to have a different client virtual drive compared to the sequencer then testing will be paramount.
Yes, When v4.5 is released we will support the client upgrade from 4.2 and respect the settings.
[update 8th Nov]
Ok, so what about your sequenced applications, will they work? Yes, we expect applications sequenced in 4.2 to work just fine on the new 4.5 client, however, there will always be some edge cases and in those circumstances it might require the application to be unpacked to a 4.5 sequencer, and then saved again (not re-sequenced).
As with previous updates, it is recommended practice to upgrade all the clients first, then the servers. 4.2 clients will not connect to 4.5 servers, 4.5 clients will connect to 4.2 servers.
An application would also need to be re-sequenced (or upgraded) if you wanted to use some of the new features of 4.5, for example, multi-language support, dynamic suite composition, etc.
I don't normally advertise what's [hopefully] already known, but, 4.5 is a big step forward, and not just in the name change :)
http://blogs.technet.com/smsandmom/archive/2007/11/12/microsoft-application-virtualization-4-5-is-open-for-public-beta.aspx