(1) Change loads: more powder ususally gets a higher point-of-impact, so try to reduce the charge.
(2) I'd be very reluctant to change the hammer by removing metal. You would need to reduce the height of the flat above the hammer, not just the notch. You could really butcher the looks!
(3) Raise the front sight. You can calculate the amount with the ratio of the front sight height to the sight radius to the amount high at the distance.
Or try some duct/masking tape to the front sight to get an idea of the amount you need to raise it.
I'd try at least 1/4" more and see what happens.
(4) I don't know how Pietta holds the fron sight. You can fabricate another higher sight from brass sheet stock. You will probably need to remove the existing front sight, maybe its a screw-in, or swaged-in. Once out, you could try to reproduce it in brass (easy to work) but a higher profile
However you remove the front sight, it is an irreversible action, so be prepared.