They did that same sort of thing on the GP heated seat switches I have. They left another pin and merely don't have anything going to it.

My belief is that this switch and or attached circuit board could have been used in many areas and therefore the pin setup is a result of that.

I like the idea. Just get that trim piece cut out and on to make it a perfect mod. I'm guessing that you'll have to be pretty careful while cutting the vent piece up. They can be somewhat brittle. Maybe use some heavy tape on the back during cutting.

sounds like you need some SEM paint and a bit of JB Weld to make it just right.