it will happen, but may or may not happen quickly. if you have the beer in the keg equalized at 30 psi, and if there is a lot of head space already with pressure at 30 psi, this may take a bit. when you switch to the 2 psi regulator, that regulator should, as i said, should remain closed. in other words you are not going to open and supply 2 psi gas to the keg until that head space pressure drops to 2 psi. if you have a lot of head space and pull off a beer, the pressure will drop and equalize as co2 comes out of solution to a new slightly lower pressure. with a lot of head space and high pressure this could take a bit. if the keg is completely full with liquid it will happen faster. ex. a 15 gallon keg with 10 gallons in it and head pressure of 30 psi, drops to 5 gallons of beer, and now 10 gallons of head space the pressure would drop to about 15psi i say about because that is just a basic pv=nrt without discussion of gas in and out of solution.