Indeed, in version 7.3.1 Problem 2924 "Cannot create more than one Inbound Mail Mapping for a process" has been addressed. As you'd expect, this means you can now have as many mappings as you like to the same process.
I'd recommend an upgrade rather than a database hack, I'm not aware of anyone who has done this successfully.
I thought that might be the case.
We will wait for 7.3.1 as we are looking to put this in early next year. (Hi David )
Morning Stuart - I think you are really going to like WebDesk :-)