If you have skills you can mod the brush holder/regulator assembly. Depending if its an a or b type regulator one brush will be ground or pos and other brush will be the field wire to the regulator.
Or find out if other regulators are available for the same family of alternator as you have. With non pcm controlled internal regulators there might be a few with different voltage set points to choose from.
what are you trying to accomplish? Don't believe all the hype about increasing your voltage. Your lucky to see 100 amps out of your stock alt at idle and if you're pulling more than 100amps then you will be seeing only battery voltage anyway. The only way it would help is if you had a bank or two of Maxwell caps.