Well, als you can see from the helpfile that's nonsense. Maybe they have to do it because it's coupled with some automated software to add a license to some vps or server. Only reason I can think of.
However, you could use the admin backup/transfer to backup admin and all resellers and accounts.
Download all backups, have them install the OS with DA new like they want to.
Then fix DA again, like enable SSL and DKIM and all other stuff you want, and then restore all accounts again.
Not my favorite solution, but if they refuse to change the license id...
You could point them to the help file I linked to about changing licenses. But if they don't want to give that kind of support, not much you can do.