We are soon upgrading to QC 9.2 from QC 9.0. We will uninstall the QC 9.0 from the server and install QC 9.2.
Do we need to change anything on the desktops? Can we keep using the previous client piece (of QC) as well as previous add-ins installed on those desktops?
For the main QC application, any changes will be downloaded via ActiveX controls on the first access to the site from the client system.
Without knowing the specific addins you have installed it is going to be hard to answer if they will need an upgrade. The only thing I can say is you will need to check the Addins page from the main QC entry page link to see what you have installed needs updating. Although with only a .X jump in revisions, I don't think you will need to do any updating.
Insanity: doing the same thing over and over again and expecting different results