I'll reply to my own post. If I choose the same ssl type and give it the exact same name it seems to latch back onto the file, so this isn't as bad as I thought. But still... a way to import multiple ssls from .ssl files back into a project would be very nice.
I'm not at a Rh machine to check where the link is stored but this should work.
Move the old layouts from the project.
Recreate layouts with the same character perfect names. Leave default settings.
With Rh closed, open them in a text editor. Do the same with the old files
and copy the content across.
Backups everywhere of course.
Just for the people among us who like to dive into source files: You can update the rhlayout.apj file manually to get them back as well. Don't forget to trash the CPD.
Thanks. I figured that out as well yesterday when it happened again.
Restoring the rhlayout.apj file from my backup made it so I didn't have to retype each layout filename.