Well, as usually happens, other accomplishments have made this line of inquiry obsolete.
I am currently using a 5 megohm resistor for R14, and it seems to be what I wanted. It puts the high battery voltage trip point up to about 68 volts. This is extrapolation from voltage drop readings across R14 as don't want to run my batteries that high just to test the setpoint. On 24v units it would trip at 34v and 17v for 12v units. (Piggybacking a second 10 meg resistor to the original 10 meg resistor gives an easy to do 5 meg R14)
The other part of the problem is the spike issue discussed previously will still cause a trip now and again. Also, the temperature sensor for heatsink temperature that plugs in to the control board near the plug for the main fan affects the high voltage setpoint. It shouldn't, but it does. As heatsink temp increases, so does the voltage drop across R14, pushing the unit closer to trip than it should be.
Since I had already added independent fan control, unplugging the stock heatsink temp sensor stops that problem. So with the 5 meg resistor at R14 and the sensor unplugged, my pj runs without tripoffs so far. The spikes can still get you, although much less often.
So, it can be done this way, but an occasional trip is still one trip too many in my book, so the zener diode is still the best solution overall. As long as not having any high battery voltage trip is ok with the user. Honestly, if your system is set up properly, a high voltage trip is unnecessary.
While arriving at this point, Oztules, Clockman and others have perfected a better control board, which I will be switching to as soon as I can. So I guess that's it for this thread....