It seems like you should be able to do this via the admin panel as it states in the tools section when you click on a table:
Edit Forum Table Definition[/url]
Below is all the columns in your Forum table. By clicking on one of the column names, you can view more details as well as alter the column definition.
But at least in my installation which is the following versions:
Gossamer Forum Version: 1.2.1
GForum.pm version: 1.131
GT::SQL Version: 1.101
GT::Template Version: 2.106
You cannot actually click on title of a column as the instructions indicate. It shows them all but they are not links.
There seems to be no way to do anything but add an additional column, but nothing about changing the properties of an existing one. It seems at least at this point it would have to be manually changed in both the def file and the actual DB itself via a DB Admin Tool.
May be a bug in the admin interface that they are not showing as links so you can modify both the DB and the Def file from the Admin interface.
Herpeton
VegPeople.com