Hello,
I didn't see the reference to mxAutomation, it's a bit different from RSI. You can use RSI not only to control the robot in real-time, but it's actually primarily used to offset the tool in realtime, just like you would need it.
How "hectic" is the movement of the plasma torch height control? Because if it does not have to react superfast, my idea would be as follows...
So let's say a line looks like that...
LIN {E6POS: X 86.613, Y 516.346, Z -73.467, A 89.987, B 67.155, C 51.078, E1 0, E2 0, E3 0, E4 0} C_DIS
Then you search in Notepad(++) for ", A" and replace it with "+ PLASMAOFFSET , A " so that the line would look like that...
LIN {E6POS: X 86.613, Y 516.346, Z -73.467 + PLASMAOFFSET, A 89.987, B 67.155, C 51.078, E1 0, E2 0, E3 0, E4 0} C_DIS
You will need to set the PLASMAOFFSET variable in the sps.sub cyclically from your analogue value, probably with some scaling and safety measures so that it does not move too much.
The robot will read the variable in the advance run, so you will have some delay, and you will need to create toolpaths with very fine spacing to reduce latency.
I haven't tried that out, so it's entirely possible that it won't work. But you might give it a try.
However, my gut feeling would be to simply do that with an external microcontroller. Get an Arduino for 10EUR, a stepper driver for 15EUR and a linear stepper for 30EUR from china, and something so that the analog value coming from the plasma torch does not fry the Arduino. And then plenty of time to set it up

Best,
Johannes