Heard a lot about grinding/sanding the lower lip portion on Pop-R's so they perform differently than they do out of the box.  

Got any info on what all the discussion is about and what it's intended to do to the bait by modifying the lip?  How much are you taking off if you do mess with it?

I do that to most of my Pop-R's to get a non-POP when worked. It ends up looking somewhat like the Japanese poppers. I file the lower part until it is about the same as the sides. It is more of a spit instead of a pop which closely resembles the actual sound of baitfish on the surface trying to escape from feeding bass.