Hi I'd like to change the output voltage of the gel electrophoresis power supply so that I can use it with a box with larger separation between electrodes

From your pcb diagram and the explanation here:
http://public.iorodeo.com/docs/electrophoresis_power_supply/intro.html

seems like the way to make it so that the output voltage could be 150V instead of 100V is by altering the voltage divider made up of
R2(1MOhm) R3(15KOhm) and RV1(0-50KOhm).
Vout = Vref (R2/(R3 + RV1) + 1), as you report this formula gives a range of ~25-100V.

If I alter R3 to 10KOhm I get ~27-150V as the range. As far as I can tell I think the rest of the components can handle this - am I correct?

any help would be great