If this desired voltage modification is intended to better recharge distant depleted batteries over a thick copper circuit, be aware you should not Idle parked to recharge for more than 10 minutes or so as the alternator can easily heat upto the 220F danger zone.
I can spin a dial and choose any voltage I want, and if maxing out the alternator at idle its stator will raise above 170F in 5 minutes and is still heating quickly. Sub 25MPH driving does not do much either in regards to keeping stator temperature down, but 65MPH freeway driving it will not rise above 132F when maxed out, or nearly so.
I had to trick my engine computer with a 50 watt 10 ohm resistor into thinking it was still connected to the alternator, and I use a Transpo540HD external regulator. It has a potentiometer for voltage adjustment. I snipped the pot's legs and added wires and a larger 10 turn potentiometer so I can easily change the voltage while underway.
About 2/3 more amperage will flow into a battery at 14.7v compared to 13.6v, so it is a very worthwhile modification when one is regularly deeply cycling batteries and wanting to take advantage of a rather large amperage potential charging source.
I've put a digital ammeter on my dash, next to the voltmeters and find it enjoyable to watch amp flow into the battery change with different electrical pressure( voltage) reaching battery terminals.
The battery(s) dictates how many amps it accepts at the voltage reaching the terminals, so in the case of recharging deep cycle batteries an alternator with external regulation is much more desirable than one meant to simply replenish what a starter battery requires, as most vehicles will quickly lower voltage to the Mid 13's so as to not induce overcharging or excessive water usage. Vehicle Voltage regulation was never designed for fastest recharging of depleted batteries, and 80% charged to 100% charged, basically takes no less than 3.5 hours, and this is at ideal voltages reaching battery terminals.