Yes, the PRV would open, relieving pressure in the boiler,, the supply line from your water supply would sense the drop in pressure and add cold water to the system.. the water temp in the boiler would drop.
I run my boiler at 165* in the summer, with 25* differential temp spread.. so it starts the combustion fan/auger/stoker when the water cools to 140*, turns off at 165*.. if my timer cycles for it's 1minute burn just after the aquastat just shut off, I might see 180* water temp. but nowhere near the 205* I have my high-limiting aquastat in the timer circuit set at... so I don't have any over temp spiking problems..
It would not be difficult to add a strap on make-on-rise aquastat to the system and use it to trigger the system to circulate the water.. I'd use the whole house or a basement circuit.. I originally planned on using my shop as the dump zone, untill I found out it was a problem for wood systems, not stoker coal boiler systems.. so I don't have any dump zone.. But some installs may need one or owners feel better having one.. personal prefferences.