Nope, it's best not to add custom code to the forum's script - I learnt that the hard way, and repeatedly too! Such scripts are frequently updated (this one is already out of date as they're on version 5.0, this is 4.2, though possibly because they're using the "publishing suite" which includes a blog?) and any custom code is either lost or can cause real problems.
The thing to do is update frequently and use the features, but certainly vBulletin has some strong moderator goodies built in. There may well already be an auto-setting to block reported posts? If so they deffo need to switch it on,