external.php - excludes specific forum categories
 

I'd like edit the RSS external.php file so that it excludes specific forum categories - not sure what part of the code I need to edit though.

You could set forumids=1,2,3 in the query string for forums you want to appear, or you could make a plugin at the external_start hook, and set $forumids = '1,2,3'; for the forums you want to appear regardless of what comes in via query string.

On second thoughts being 'forum specific' (rather than exclude forums) is better for me. I'd forgotten you can specifiy forums in the URL.

"you could make a plugin" - never done this before so I'd have to read up on it.