[kh99]

Originally Posted by X-or

should be something like this
UPDATE vb_user SET usergroupid="n" WHERE .... and that where I'm lost, it should be possible to ask that whenever you have userid=X and field2= a certain value then move the user with that userid in vb_user table to banned group

UPDATE vb_user LEFT JOIN vb_userfield USING(userid)
  SET usergroupid=N WHERE field2=Y

2) related, these spamers filled the homepage field to promote malicious websites, so I want to delete the homepage field of all spamers, it should be easy enough to cook a query and apply it on all users of banned usergroup once step 1) is done

Assuming step 1 has been done,

UPDATE vb_user set homepage='' WHERE usergroupid=N

'' is two single quotes, i.e. and empty string.

3) unrelated, I had issues with default option at registration due to some addon, but I only noticed recently so I want to force the default options I really wanted to have on all users of the most common group (registered users)
Here are the options I want to force to Yes:
-Receive Private Messages
-Send Notification Email When a Private Message is Received
-Save a copy of sent messages in my Sent Items folder by default
-Enable Visitor Messaging
-Display Signatures
-Display Avatars
-Display Images
-Display Reputation

And also:
Automatic Thread Subscription Mode -> Instant email notification
Message Editor Interface -> Show Enhanced (WYSIWYG) Editor Toolbar

Please help, thank you very much.

A lot of those can be done by going to the admincp, Maintenance > Execute SQL Query and finding the query under "Automatic Queries" (you need to have your userid in the config.php file, in the $config['SpecialUsers']['canrunqueries'] variable, or else have the site in debug mode). If I have it right, that leaves:

-Save a copy of sent messages in my Sent Items folder by default
-Enable Visitor Messaging

that can't be set with an automatic query from that menu. When I get a chance I'll try to figure out what the queries would be for those.