>In my setup I'd like to make a backup of what was already installed. So if there is a problem with an installation I can get back to the previous content of given folders.
>
>If not possible with InnoSetup is it possible to do it with another installation tool?

I don't use this Inno, I use Wise and it has a Rollback option that does this almost automatically. Unfortunately, it is no longer available for purchase.

Have you seen this link.... it might be what you are looking for to help you:

https://adventuresinscm.wordpress.com/2013/09/09/inno-setup-restore-files-on-uninstall/