from your question it's not clear if you are talking about MWG 6 or 7, but I assume it's about MWG 7 as your other questions in the past dealed with that.
The Log Handler in MWG 7 is based on rules, just like the other rule sets. The one that writes the Access Log can be found under Policy > Rule Sets > Log Handler (the bar at the bottom) and then in the Tree View under Default > Access Log.
You can edit the rule set and insert conditions, or you could add a rule that will stop the rule set when a certain condition is met. You didn't specify what exactly an invalid rule would be and there is no default property that would indicate something like that, so I can't create an example for you here.
It's MWG 7, if a user incorrectly enters a URL this gets logged and reported as an uncategorised URL in reporter, at the moment I don't log 407 status codes using "Response.StatusCode does not equal 407", so I'm looking to do something similar for incorrect URL's