Be careful with those gage sets. At the ports, screw in the valve just enough to open the Schraeder valve, maybe 1 or 2 turns after you see pressure on the gage. If you over-do it (like most people), the Shraeder valve often gets bent. You can usually use needle-nose pliers to re-bend it so it doesn't stick open, or at least pull the stem out so it stops leaking. I think you can also get caps that will seal the port even if it leaks.

If determined to replace it, know that even if you totally remove it, it might take 2 min for all the refrigerant to escape since it must boil off to do so. I have replaced one while venting only ~2 sec (negligible loss). I used a nice tool from auto parts w/ a big brass cylinder for your fingers, but you even see removal tools in dust caps for bicycles. Use an AC Shraeder valve, not one for car or bike tires (rubber will degrade). BTW, compression gages use a very special Shraeder valve (white plastic) w/ very weak spring so they don't affect the reading (acts as a check valve). I bet many people install a regular one and wonder why compression reads low. EPA rules make it illegal to vent any refrigerant to the atmosphere, so hope their drones aren't watching. True, even for the HC refrigerant I use, which is the same environmental impact as a cow fart, and they vent all day long.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans