I have never found a Rem receiver to be case hardened????
They are always quality heat treated through and through. Have you witnessed any that were case hardened?
It may not effect the receiver integrity enough to cause any problems but rest assured if you cut a knotch between the lug recesses, you weaken the receiver to some degree.
My point is that with the WSM there is no real reason to do this, you can make a modification ot the bolt stop and get enough bolt throw for these rounds, again, unless you use a very long throat in your chamber.
If there is no need, why make the cut when modifying the bolt stop is much easier and has zero effect on receiver strength?
Kirby Allen(50)