OK, thanks! I had planned to remove the old DAT tree, apply the script for a new tree, just like you suggest.
HOwever, I thought I had to move the old ROM tree to the ToSort, and create a new folder rom tree using the move scripts and then let RomVault do its thing. But then it would recheck all files crc again, taking ages.
I'll try your way, seems logical but I have had RomVault leaving a lot of trash behind when changing directory structures. Here's hoping this has improved in the last few years.
Thanks for the tip!