Ike -- You want to change the pitch only, not the span, right?  Fill the hole with plug material to about 1/4" below the top of the hole and let it set up.  Then set the drill up to go exactly into the old hole and drill with the new pitches.  There will be no external evidence of the change and if you use clear plug it will be almost invisible inside the holes.  When I do this, I rough the inside of the hole with 100 grit sandpaper and cut a couple of shallow horizontal slits in the side of the hole that will have the plug left after the redrilling, using a Dremel tool with an abrasive blade.  This will create quite a bit of smoke, as the resin melts some - don't breathe the smoke.  I've only done this on holes for grips, but from the appearance of the hole before inserting the grip, I feel sure it will be smooth enough after a little sanding to work without irritating your finger tips.  --  JohnP