Welcome to the forum @TallSteve
How the backup process works shows the filelist.json that’s in the dlist file.That’s probably the big pain.
While converting paths can be done with a sophisticated find-and-replace, and the dlist zip file updated and AES-encrypted, there’s also a Base64 of the SHA-256 hash of the dlist file in Remotevolume table. Going through the steps to edit that is possible, but I don’t know how many dlist files you’d need to “fix”.
–skip-file-hash-checks might be the way to temporarily suppress the usual hash check of hacked dlists.
For simple restore from old drive, I think it will restore the files to some other Linux folder of your choice without any messing around at all, e.g. by using direct restore. Windows permissions are lost of course.
If you want to backup continued changes of old drive, simplest solution is to start a new backup, e.g. by importing your edited JSON config export, then recent restores are easy, and old versions as by above.
If you’re really adventurous, and really want to avoid uploading things again (and keeping two copies of basically the same files), you might be able to get Duplicati block-level deduplication to attach still-valid blocks from the destination, just as would happen if you moved a file to a different folder. Its data blocks will be determined, found to already exist, and referenced without having to upload them again. The old location looks like a deletion though, so be careful about retention policy, or you might lose old versions.
I think I once played with a workaround for a totally missing initial dlist file (it goes up late) by building a dlist file with empty JSON (maybe []) for filelist.json, then running Database Recreate to record blocks. Setting –no-auto-compact ensures it won’t reclaim any “wasted space”, then backup to reattach blocks. This scheme isn’t directly well-suited for your use, but you might be able to figure out how to adapt it…
If you get adventurous with this, backing up current backup could be done as a precaution against loss.