The process I outlined should clone the new AP's configuration to the older - already mounted - AP (so it would be back to the default settings with a username of admin and a blank password, like the new one), not the old to the new.
AP Manager doesn't ask for the password during discovery, only if you double-click on the device to access the AP Manager configuration pages (which are much more user-friendly than the web configuration pages, btw). It does not ask for a password when you right-click the device and choose CopyCFG, so I don't know if it would for PasteCFG. There has to be SOME way to reset the AP to defaults though.