Can I "roll back" from P3Dv5.3 to an earlier version?

Hello there!

It's unfortunate to hear about your lost scenery add-ons and backups after upgrading to P3Dv5.3. I understand that you're looking for a solution to either use contemporary add-ons or roll back to a previous version of Prepar3D to reinstall your desired scenery. Let's explore a couple of options:

1. Alternative add-ons: I would recommend searching for more recent and compatible alternatives to your older add-ons. The flight simulation community is continuously developing new scenery and libraries, which are often optimized for the latest versions of simulators like P3D. You may find a suitable replacement for the NZNR scenery and the Vector Land Class Object Libraries that work smoothly with P3Dv5.3.
2. Manual installation: Instead of rolling back to P3Dv3, consider manually installing the required libraries by extracting the files directly into the appropriate Prepar3Dv5.3 directories. This may bypass the issue with the installer not recognizing P3Dv5.3's installation path. However, there may still be compatibility issues between the older add-ons and the newer simulator version, so this isn't a guaranteed solution.

Rolling back from P3Dv5.3 to an earlier version is generally not recommended, as it may create further compatibility and stability issues. If you choose to go this route, you should be prepared for potential complications and may need to reinstall all your add-ons from scratch.

In summary, I'd suggest looking for newer and compatible add-ons or trying the manual installation route. Rolling back to P3Dv3 should be considered a last resort, as it might lead to more challenges.

I hope this helps, and happy flying!