REINSTALLMODE
InstallShield 2020 » InstallScript Language Reference
This system variable is non-zero if one of the reinstall functions has been called in an InstallScript installation—that is, if FeatureReinstall, FeatureUpdate, or FeaturePatch have been called in the current instance of the installation.
Project:In an InstallScript MSI installation, this system variable is non-zero if the FeatureReinstall function is called. FeatureUpdate and FeaturePatch are not defined in an InstallScript MSI installation and should not be called.