I actually owe an apology. During the changes through testing/beta here, I did in fact break linking with existing accounts.... .... but it was for the best in the end, because I re did a lot of it in the fix. There are now more info screen to tell the user what's going on as the hook acts.
Linking accounts now points off to standard login on submit. If correct user/pass, you'll see the standard phpbb-you're-logged-in-message, then the hook will inform them they've linked.
Revoke button has been added to the board preferences screen in ucp. If no access token is available, it just says to go to fb app settings. If one is present, it send the command itself. If user is not fb connected, a connect your fb account button is displayed instead.
I've tested and retested in svmods and it seems to be running pretty smoothly. Test away, let me know if anything is wrong.
Special thanks are due to 'Saugata Datta' for doing some work for me: he threw a modx in with the beta files, and confirmed it was all auto mod compatible. I just need to replace the file and edit/add a little to the modx file and we can call it an RC