in the current build of ic2 classic, there seems to be no way to do this; maybe you could add something similar to the nuclear control thermal monitor?

@escman1999 Machine Tool to set the Comparator Output, and then a comparator or adv comparator to get the output you want.

hmm, i was thinking like, a way to shut off a reactor when it reaches say, 5000 heat. world control can do this, but it's extremely buggy and crash prone

You have 16 stages based between 0-15 no heat to max heat. I assume with a bit of work you can easily make a redstone signal hit the heat you want to. Get creative.
IC2C gives you all the tools to achieve that. But thinking is required.