Hello VM-Steve,
Welcome at the vmware communities forum.
VMware Fusion 2.x is not supported on mountain Lion and I doubt that it will even install.
You can of course run your virtual machines made with Fusion 2.x in newer versions of VMware Fusion, but I don't think that the "one time change" that you mention that Fusion made is causing you the trouble for trying to force installing an old version onto mountain Lion.
Virtualisation depends strongly on features in the operating system and is therefor quite tied into specific OSX versions.
An old version like Fusion 2.x has not been updated to work with mountain lion.
The best remedy here is to run a newer version.
My advise is to get the trial license for Fusion 5 and run that to see if it pleases you.
You got 30 days to find out.
--
Wil
edit: To give an answer to your question.. dragging the installed Fusion to the trash can should normally be it. But.. here's the more complete answer: http://kb.vmware.com/kb/1017838