I only really have one set of piercings - lobes. They're at 0g right now.
With hider plugs you can barely tell they're there :
That's super up close and sharp - it's basically invisible from further away, and I could even go over them with liquid latex and blend in with makeup if I wanted to be absolutely seamless even on that kind of close-up photography.
I have about 22 hours of tattoo work and that doesn't really cover a lot. I haven't had a costume where they'd show so far, if I ever did I'd probably do a nude fabric covering or makeup if that wasn't possible. And since I'm not really comfortable showing a much skin (inked or not) I'd probably make a nude shirt if I had something open that far, anyway (I'm not really "modest", I just feel really weird and exposed with even bare shoulders).
I don't think there's anything wrong with showing them during cosplay if you want to, just discussing/showing some of my ideas for others who might want to hide them !