You can deregister the Sony by hitting ctrl-shift-E to ADE (cmd-shift-E if using a Mac) with the Sony plugged in.
Then restart ADE, and reregister the device with the new AdobeID (that is, the AdobeID currently registered on ADE itself).
If you reauthenticate with a new Adobe ID, you will no longer be able to read any of the DRM books already on the device.
I can't see any way to find out which AdobeID you are currently registered with (I can see the uuid but not the user name).