Flywheel

Has anyone tried and succeeded at drilling the stock flywheel to lighten a bit? Tempting but possibly dangerous…

Super dangerous.

If you're racing, not only should you have a billet flywheel, you should also have a scatter shield.

The totally negligible benefit you might gain isn't worth your feet and/or the rest of your car.
 
Unless you have the tools, equipment and know how to do it properly and rebalance it appropriately I wouldn't touch it.

If a lighter flywheel is a must for you, find an appropriate replacement part.
 
Stock flywheel is 20ish pounds. And aluminum one with the steel insert is 14 ish pounds. if you want to lighten up a flywheel that’s the correct way to do it. I cannot see one real advantage on the street but in auto cross they do help.