I got it!
Once I found out WHERE PHPBB3 did username checks, I got it all together after that.
This was tested on STOCK PHPBB3 (not for DF) and Roster 2.
This should work with roster 1 as well, since it's still the same table and field.
(roster_members and name)
Would like to hear from Roster 1 testers.
BTW thanks go to WoWRoster and forum members.
This was the MOST active forum in which I posted this to, despite not much helped in the end, members here ATTEMPTED to help. (unlike other forums)
It did however inspire me to make the brain hurt a little longer and resolve it. lol
ABOUT THE MOD:
This is mod to the PHPBB3 files. During registration this will check if they are a VALID Guild Member, and disallow all those not a Guild Member.
This allows less administration, as well as forcing users to use a "Character" name, as opposed to some name no-one knows.
REMEMBER TO BACK UP YOUR FILES BEFORE MODDING!
note: Both WoWRoster tables and PHPBB3 tables MUST be in the same database for this to work.
No coding for cross database checking will be done.
Enjoy!