FWIW, as a distributor of the product, I can tell you that the relief valve is stamped as 15psi. Anything in excess of this level will vent off. So, one could argue that it is also a safeguard AGAINST excessive pressure buildup in the headspace of a warming growler as the CO2 solubility...
Yes, it is possible. The Growler Saver features a pressure relief valve set at 15psi, so you won't over-pressurize the growler vessel. You might need to periodically "top off" the growler with CO2 until it reaches carbonation stasis, as head pressure could decrease each time as the carbon...