Do I need to create a separate SilentInstall-SPB.INI to install Hotfixes (ISRs)?
No. With the introduction of the Silent Installation method in 17.2 (and future versions) installation of both the base release as well as any updates can be completed with a single INI file.
Is there a way to silently uninstall the OrCAD products?
Yes. Assuming that the products were installed silently, modify your silentInstall.INI file for the which reads “OnMaintenance=MODIFY” so that it reads “OnMaintenance=REMOVEALL” and the installation program becomes an uninstallation program.