Exactly how to do it, only thing I've done differently, was to use a plastic trim tool.

 

I added Platinum leather arm rests to my door panels and that cover no longer snaps into place fully since the leather is a bit thicker than the molded plastic XL pieces. I guess I could order these covers for a platinum that would've included the leather but meh, it's not a big deal. I do hate the fact that the plastic scratches so easily tho.