Most of the customs I've seen for sale have shafts at least 13mm if not bigger. I'm told smaller shaft cues don't sell as well. Question: How much price difference, if any, does it make?
It seems to me if you alter the size of the shaft, you are limiting the prospective buyer pool. Also, a collector would want the cue in original condition, if possible.
Couldn't the shaft be small and original?