how about sanding or cutting around the bat to make it smaller , not the handle. If I buy a penhold bat and sand it a bit smaller, will the bat be damaged ???????
I would mark it, then sand it with my belt sander. You always finish with sanding to get a smooth edge anyway. For 4mm you can use a fine scroll saw to cut off maybe 3 mm and then sand down the last part by hand.
Shaving or using a normal saw will do to much damage to the blade.
Definitely sanding .... the blades are made from soft woods so there will be no problem .... i suggest to use 120 grain in beginning if you want to grind more and finish with 400 grain .
And yes draw a shape before you start .