Trimming 1/2" off a golf shaft will cause the swingweight to drop by 3 points. For example, D2 to C9. Also, trimming 1/2" will flatten the lie by 0.75°.
Before you start cutting, hit some shots with face decals on different irons: If you hit a lot of shots toward the heel, the shaft may be too long. Also, use sole tape to see if your lie angle is proper for you.
If you're not familiar with the tests, have a good clubsmith help you.