Backup the registry branch and restore it on the new machine/install before starting the installer.
If you also backup the whole Plex data folder and move it to the new machine, your users won’t even notify that something changed.
https://support.plex.tv/articles/201539237-backing-up-plex-media-server-data/
If you move the Plex data folder to a separat hard drive/SSD beforehand, the process becomes even simpler, because you can grab this drive and move it to the new server. Asssign it the same drive letter as before.
Then restore the registry branch and install the server software. Done.
