yes it will mess up your regulator. unless you have a check valve in your gas shutoff. Most cheap homebrew store shutoffs don't have one built in, you really have to look for it. You can restore the regulator if you unscrew the regulator face and rinse out with PBW and a turkey baster. Keep the dials upright. Good as new. I only know from that one time using a beer-ruined regulator racking using co2 x carboy cap. The low side on the regulator shot through the roof suddenly. That disproved another theory, you cant blow up a carboy that way, the carboy cap blows off first. Makes you think you've been shot though when it happens. That was a 'universal' cap on a 5 gallon carboy. Not sure what would happen with a threaded neck carboy and I don't plan on testing it.