Well, not quite what I had asked, anyway good to know that any other location is possible!
To me however, that 'Old Path' isn't any older than your current MC version, thus should be usable as any other of MC's sub directories - and if you upgrade, MC will import your librarie(s) to the 'New' folder in App Data, or no?
If this was a saftey precaution, MC would store libraries elsewhere (other than App Data) by default, would it not?