You definitely should not crack the fitting on the TX valve, which is on the firewall, just below the charcoal canister. It uses an Allan key screw to clamp down the fittings. You need to remove this when doing a heater core, but doing so will cause all refrigerant to escape once you loosen the fitting enough.
If you were to crack the bolt loose enough to allow refrigerant to escape, you should drop your tool and evacuate the area for 5 minutes. By this point all pressure in the lines would have escaped.
But you should definitely not do it, this information is just to make you aware of places you should *never* fiddle with unless consulting with a professional first. Captain Planet will thank you.