putting a hole in your cap is no problem and will not cause any problems
This is From MSD.
Ionization occurs when the air inside the cap
becomes electrically charged resulting in spark scatter
or crossfire. It is more prevalent in smaller caps and
again in areas with higher humidity. MSD rotors are
designed with high vanes to help stir up the air
preventing a charged area from building up. For more
prevention, you can DRILL VENT HOLES in the cap to release
the pressure and to introduce fresh air. The holes
should be at the height of the rotor skirt and at least 1/4"
in diameter.
