I'm pretty sure tweaking the outdoor reset curve does not qualify as "working on gas appliances" any more than turning the temp up/down on your gas oven would be.
Monkeying with the gas plumbing or venting, or repairing a faulty boiler ignition would be outside the legal bounds. Even swapping a thermocouple on a standing pilot ignition is a technical violation, not that anybody is going to write you up for that. Re-lighting your own standing pilot is probably pushing the envelope too, not that you'd be written up on that one either. Messing with combustion blower settings on an ALP or some of the other setup issues might be technical violations, and may have safety or longevity consequences for the boiler.
I too am curious as whether the landlord has issues with making adjustments without prior permission/discussion with both the landlord &/or a boiler tech. The whole installation is suspect, given that the installer (as reported) neglected to install the code-required tempering valve on the indirect, and the fact that they installed a 3-speed pump on the indirect loop rather than just specifying the correct single-speed, and that it was initially set at a speed that short-cycled the boiler. It wouldn't surprise me if the whole thing was a bootleg. Any inspection tags in evidence?
Anything you do that is dangerous and caused damages or ruins the equipment would be some liability issues. If the thing was installed improperly and causes harm or self-destructs that's going to be on the bond of the licensed installer. Setting the outdoor reset curves to something other than the default settings is neither dangerous or damaging to the equipment. About the worst that would happen is if you set it so low that it's short-cycling like crazy, putting a lot of wear & tear on the boiler. That's not dangerous, and sadly, many licensed-bonded professionals in MA have left boilers set up to short-cycle themselves into an early grave.
Disclaimer: I'm not practicing law in MA nor am I a MA licensed gas-fitter or plumber.