There is no USBC rule concerning how close to the pin, or drilling the pin out.
However, for warrenty issues, you should follow the instructions on the box or drilling instructions concerning how close to the pin (primary and mass bias/PSA) you can be and not void the warrenty.
I know, from my years at Brunswick, that you can drill the pin completely out of a Brunswick ball and not void the warrenty. Just make sure that you hit the center of the pin when drill it out so there is no pin left.
The drilling you mentioned, and just looking at your specs., the Cell drilled in the manner you described should give you a fairly even reaction with a strong, continuous backend. This ball is not designed to give you a big skid/snap reaction.
I hope all of this helps.
Verbs
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Larry Verble