I would go with the instructions. I didn't cut mine when I tossed a new pair in my new goalie skates and I think they packed down a bit now they have a little kink in the heel that bunches up and hurts. I would go ahead and cut it because 2mm isn't that big of a deal. Or maybe cut it down half the recommended amount, try it out for a bit, and if it packs out you can trim it a bit more.
09 Burton Supermodel X 164
11 Burton Hero 158