The account refusal message is set in ~www/php/website/config.php via the accountRefusalText variable.

If the groups table in the auth_N database has a non-empty accountRefusalText field, then the value of that field is used as the message.

For example, the CHESS instructors group has a non-null accountRefusalText value.

To edit the database, you must be in the webmaster group of the website. The user interface may be found at http://chess.eecs.berkeley.edu/mysql or
http://embedded.eecs.berkeley.edu/mysql or
http://www.e3s-center.org/mysql or
http://www.truststc.org/mysql.

Click on the auth_N link, where N is 2 for CHESS, 3 for Embedded, 4 for TRUST and 5 for E3S.

Click on the groups table and then click on Search and edit the groupname field to find the workgroup in question.

Click on the pencil icon to edit the row.

Find the accountRefusalText field at the bottom and browse to the new text to be updated and hit "go" to save the text.