[Opserty]

Add an extra column to the forum table, then go edit the forum in vBulletin AdminCP...just change a setting then edit it again and change it back. That should refresh the cache I assume. Then run a var_dump() on the $vbullletin->forumcache, see if you column is listed...I'm pretty sure though that vBulletin will select all of it, if not there may be a hook you can use to alter what is fetched.

Finally, you should avoid editing the vBulletin PHP files, there must be a hook in the forum datamanager...like forumdata_... I'd be surprised if there wasn't.

Also I recommend you check out the articles section there is loads of stuff you can read & learn.

Using the vBulletin Input Cleaner