Haven’t found that yet, I don’t think you can as the query builder won’t let you modify the equal operator to a not equal. What I do is set create a point group “Bad codes”, move it right down to the bottom but above _All points, and set its layer to “Bad Codes” . When the points have been imported, isolate that layer and you have all the mongrel codes on the screen. Allocate a very visible point style (large symbol with skull and crossbones maybe) and/or label style that highlights the bad code, and you don’t even have to isolate the layer. If you click on the the point, the properties window shows it up as a bad code by showing the layer name. That’s the best I’ve come up with.