:welcome: aboard Merc Ken. Always nice to have a new member join us...
There are two points of view with your questions. Some people simply clean the carb(s) and install new kits in them, but don't remove the welsh plugs or anything else other then a general disassembly and good cleaning. And if your engine wasn't doing anything really weird, that could be all you need.
And then there are those that remove everything for a good thorough cleaning and reassembly after every little passage if verified clean and open. And that would be removing the welsh plugs and even the plugs if their carb had any.
If your carbs are seriously dirty, I would remove the welsh plugs while cleaning them but maybe not the brass plugs. WHY? Because welsh plugs are fairly easy to install new ones and seal up well again. Not so sure about the brass plugs though. To remove a welsh plug, take an awl or little nail (sharpen if you can) and pierce the welsh pug and pry it out. They come out pretty easy that way. Just be careful when piercing the plug not to damage the body of the carb. When installing a new one, use a punch about the size of the plug and tap the domed top until you see it seal around the edges again. Some people even use a little lacquer to seal the edges. But that is up to you.
I will say most of the time I don't remove the welsh plugs because the carbs were not giving me any issues after re-kited. And therefore I just run them again. But if you are fighting an idle problem or something like that, I would remove the welsh plugs as well and make certainly those areas and the tinny holes they are sealing are open as well. I take one strand out of a piece of stranded copper wire and use the one strand to push through the little holes to make sure they all are open and cleared.
But everybody has their own ideas and probably will chime in here soon. JMHO
They are only about 1/16" in diameter. I believe they are there to fill the holes from factory machining.