[Hemicolt]

That's the worse place to have a tear. Pete is right, I think you could continue the slot on forward and get rid of the tear, but then you will have a void in front of the lift gate rod.
The rubber is like a piece of aluminum with a crack, it will continue if you don't stop it. The best way to do that is to have a round hole at the end of the crack. That way it doesn't have a path to follow. I would think a leather punch would stamp a clean hole to stop that.
Have you thought about asking a local interior shop if they have some type of vinyl/rubber repair process that may repair the tear? You may be able to cut the tear a little wider and apply the release backing paper to the outside of the boot and then flip it over and apply the repair epoxy.
If you can't get it repaired, you could always make a bezel with the two slots added and glue it to the top of the boot. Paint the bezel black and it could blend in a little better.
Have you tried Goo Gone to get rid of the paint specs?