Well the risk is that the power supply is capable of doing considerable damage if wrongly set, and "I've seen my tech doing this before" is a line in a song which I've heard several times, frequently following the line "I can't understand what went wrong", if you know what I mean.
Seriously though, ALL of those trim pots are there for a reason, and they can and do interact. Increasing or decreasing the voltage will increase or decrease the quiescent current load. -Setting the current trip too low or too high can result in either insufficient failure protection (although SSL consoles do have a couple of 'levels' of protection; the breakers at the patchbay being one example)
The four trimpots for that rail (some only have three... +250/263V being one, but I'm pretty sure from memory that +20V and -20V have all four) are (I think) labeled Vmax, Vout, Itrip and I-SC.
If you don't have a fairly thorough understanding of V and I and how they interact (which is the most basic law of electronics; Ohm's law) then I hope that you can understand my concern that you really REALLY might be better advised to consider having someone ELSE do this; someone with a bit more experience.
WATCHING a tech turn a screwdriver in a trim pot is one thing. -What you see is a hand turning a screwdriver. -What you DON'T see is the thought process which keeps an eye open for anticipated problems, and a reasoning which knows when to shut the power off... FAST.
-Honestly, I'm not trying to be mysterious or 'elitist'. I'm just concerned from the questions that you've asked and how you've asked them, because when I've answered those questions in the past without this amount of caution, I've -more times than I care to count- received a phone call the next day which begins: "Okay... I switched everything off REALLY fast, but when can you get over here and take a look at something".
Honestly, I believe that EVERY tech who reads the information I've already given you before this post would be able to know how to do it. -Power supplies are NOT things that you fiddle and tweak unless you have a working knowledge of electronics, and asking if 'I Max' is what you turn to adjust the +20V voltage honestly suggests to me that you don't.
Please... anyone else who thinks I'm out of line or over-reacting, feel free to chime in and correct me.
Keith