Opening an already pressurized corny?

I know this may be a stupid question but I've got a corny that I naturally carbed at room temp. I'm wanting to add a hop sock to the keg now as I noticed in my test bottles that it wasn't quite up to snuff. Is there any problem with relieving the pressure and opening up the keg to put this in? Then it's going directly into my fridge and onto CO2.

Will I notice any ill effects? Other than it foaming like mad when I relieve all that pressure?

Thanks in advance.

I don't think so. You might lose a little carbonation, but you can get it back when you put the tank on it. You'll probably have to let some pressure out in order to get the lid off.

Relieve the pressure in the keg by opening the pressure relief valve, remove the bail, and toss in your hop sack. Now onto the serious stuff.

It is important to purge the headspace with CO2 before pressurizing the keg. Open the pressure-relief valve by pulling on the valve ring and turning the ring 90deg to lock the valve open.

To purge the keg, set the tank regulator to about 30 psi and connect the gas to the IN side of the keg. Let the gas flow into the keg for about 30 seconds or so, then close the relief valve. If your keg doesn't have a relief valve in the lid, an alternative purging technique is to leave the lid unsealed to allow the keg to vent. You will need to reduce the purge pressure to about 5 psi to reduce splashing. Once the headspace has been purged (it should only take a minute or two), seal the lid. You're now ready to carbonate.

This will prevent the potential for oxidation.

You have to release the pressure. As stated.....after you add the hops and close the keg...release the pressure a few times after you hook up your CO2 tank to purge air from the keg.

A little hint about adding hops to a keg. The hops can clog the pickup tube. I welded a hook onto my keg lids and tie the hopsack to the lid with a precut length of string. This keeps the hopsack off the bottom an inch or more so that it does not get sucked into the pickup tube.

if you have no access to a welder, you may be able to set up your kegs by some other means. The keg may seal if you use very fine thread and just clamp it by closing the lid on it.

Even simpler, put something that floats well and is easy to sanitise inside the hop sack to keep it from sinking and clogging the pickup tube. A ping pong ball would work.

That would work, but I myself opted to keep the hops closer to the bottom because I did not want all the hops flavor to be on top because of the floating hop sack.