How do I use a custom action that is only run during Rollback?
To use a custom action that is run only during Rollback, you must first place it in the Execute Deferred section of the MSI Script.
Select the Properties tab of the custom action, and from the In-Script options select Rollback Only. In addition, the Rollback custom action can not run asynchronously. It also must be placed after the custom action that installs for the rollback custom action to execute successfully.