Has anybody messed around with Ruger's interchangeable muzzle brake/weight system? Ruger claims that POI remains the same with either the brake or weight installed. I'm interested in the FTW Hunter in 7prc or 300 win mag and being able to use the brake for practice and put the weight on for hunting is appealing.

No specific knowledge.  I would "guess" that if Ruger's claims are correct, and there is no POI change between brake or weight, installing the "thread protector", which obviously weighs less, might induce a POI change.

Suggest hunting and practicing with same exact rig, whatever you prefer.  YMMV.

M77 Mauser-based action is very good.  If your bolt shows a tendency to "seize-up" when pushing the bolt forward and applying upward force on the bolt handle (and thus bolt body) an easy fix is to use a half round jeweler's file (or similar stone) and gently chamfer the top rear edge of the receiver bridge housing where the bolt body is making contact.  This is easier and quicker than using the bolt to "wear-in" the area and saves wear and tear on the bolt body.

Strongly suggest you pay attention to torque values for all action screws and use proper torque wrench/tip when tightening them.  Torque values listed in owner's manual on pg 22.