Update database from external pages?

[forcerm]

My whole website is powered by vbulletin using the global.php hack at the top of pages

i can pull from the database using lines such as:

vbulletin->db->query_read("SELECT username FROM user WHERE postid = 1");

but how can i update the database?

i want to allow users to change the styleid from an external page, thus needing to change the styleid cell in user table.

i thought i would just be able to link to forum.php?styleid=2 etc but this only changes the style for that session, after logout and log back in it goes back to the style set in options.