Well...
It turns out if you have a HPTuners Tuner, it only takes a few minutes to change your PCM charge setpoint. No external regulator needed.
You merely load your factory tune (or aftermarket, if you have one) onto the computer, use VCM Editor to change the setpoints, save, flash the PCM, and you're good to go!
Here's a bit more detailed guide:
You'll need a HPTuners tuner plus 2 credits to be able to program anything in the PCM. If you purchased a tune through Flyin' Ryan Performance
@Flyin' Ryan Performance like me, then you already have the tuner and presumably have bought the credits.
First off, you'll want to collect two pieces of information.
1st, you need to find out what the jeep is charging at currently. For this, I recommend a dual approach. Stick a voltmeter at the battery, and use VCM Scanner to watch/graph the voltage simultaneously. Doing this, I found that the Control Module Voltage and the Battery voltage according to a relatively high end multimeter were about 0.08V apart, but otherwise fully in tune with one another. Let the jeep idle for a while, and see if there is any change. I let it run about 10 minutes. I saw no change after the starting voltage. Be sure to rev it up to 1500 and 2000 RPM. If your regulator and alternator are good, there should be no change in voltage at any steady-state RPM.
2nd, you need to find out if your jeep compensates for the temperature of the battery. Some have this sensor, some don't. I am 95% sure I don't. If as the underhood air temperatures heat up, the voltage begins to drop, this is a good sign. Alternatively, you can pull the battery and check underneath for a sensor. Thirdly, there are ways to check the battery temperature sensor temperature and voltage through HPTuners. But as mine showed up blank I have no way of saying if that's because the tuner can't access those values or because the sensor doesn't exist.
Next, after you shut off the engine, you will load your stock tune (or aftermarket tune) into VCM Editor, and view the factory PCM alternator charge setpoints.
As you can see, the factory attempts to adjust the voltage according to the temperature. I suspect the axis called "ambient air temperature" is actually the battery temp sensor. As you can see in my case, the highest temperature voltage is suspiciously close to the voltage the jeep always charges at (see above). Hence making me think there is no battery temperature sensor in my jeep.
So now it's time to change your voltage.
You'll want to choose a voltage that is safe and effective, and will protect the battery you have installed. If you have an AGM battery like a Northstar or Odyssey, the charge voltage should be between 14.1 and 14.8 volts. The hotter it gets, the lower you want it to be. Theoretically, if you did see 158 degrees under the hood, you would want 13.8 at that point. Really cold temperatures can tolerate higher charging temperatures. Note that even the factory set the freezing charging temp at 14.7. You could probably go as high as 15, but personally I would not risk anything above 14.8.
Since I have no temperature compensation whatsoever, it appears that the PCM defaults to the worst case scenario, or 13.47 volts, which is simply too low for an AGM battery to have a full lifespan. So theoretically I could just adjust all the temperatures up to the same with no effect. If your PCM actually does compensate for the temperature, you will want to make sure there is a decent slope as the temperature increases.
Knowing mine was going to default to the worst case scenario, I chose to set the lowest charge voltage to a relatively safe 14.3 volts. 14.4 is a very common flat rate charging voltage, and is not known to harm good batteries. I did slope everything else up a bit, just for completeness, but in my case this was likely unnecessary. If I actually did have temperature compensation, I would have made the slope a bit steeper.
At this point you'll want to save the modified tune as a new file, and flash it onto the PCM.
Repeat the test.
As expected, the charge voltage defaults to the worst case scenario, and the voltage remains constant regardless of any temperature changes.
And now I'm charging at a more normal voltage!