Currently this can be done only before generating the MSI, by creating separate builds in Media
page. You can then set different elements for each build.
However, we are thinking about implementing some kind of tool which can be used to modify already generated installers. Can you please give me more details about what you would need? What about the digital signature? Modifying the installer corrupts the signature and the package would need to be signed again (if it was signed initially).
You can send me an email at support at advancedinstaller dot com
so we can discuss all aspects.