Abililty to force people to change their style

1. Set all users to the new style

UPDATE users SET style="<<new style name>>"

2. Change the default

ALTER TABLE users MODIFY style varchar(28) default "<<new style name>>" not null

Replace <<new style name>> with the name of the new style as per the drop down boxes.

You can skip 2 if you don't want it to be the default...

On step 1 you can add a where clause if you only want to update specific users (e.g UPDATE users SET style="Dark" WHERE users.groups=1 to only update admin users).

Maybe table names have a prefix (the prefix is set during installation)? Then you should run a query

UPDATE <prefix>users SET style="<<new style name>>"

No problems, I forgot you could add a prefix (I've got all my various forums etc living nicely in their own mysql databases so don't use the prefix functionality)