You may modify the score for any spam rule within the Mailborder interface. Go to:
Components > Spam Score Mods
Search for the rule you wish to modify. If found, simply edit the rule and change the score. You may use negative scores.
If the rule is not found, you may add a new definition via the page menu:
Actions > Add
Simply put in the spam rule name as it appears in the Mailborder logs and assign a score. In a few minutes the new rule will propagate to all servers within the cluster.