So, there is a place where I want to add a new electrical box so I can bring in a new Ethernet port. Alas, I think this through, and is this really possible what I want to do? I’ve seen references in other places to using drywall mounting screws instead when the wall is already all finished off.
Well, let’s see. Indeed, there are quite different methodologies to installing electrical boxes depending on whether your drywall is already up or not. If it is, there are old work boxes that use a special drywall clamping mechanism. New work boxes screw to a stud. So, suffice it to say, you can install an electrical box where there is an existing finished wall, but doing so really isn’t that much different than using drywall mounting for the keystone jack face plate only.
20190615/DuckDuckGo install a new electrical box into existing drywall
20190615/https://www.thespruce.com/install-electrical-box-in-an-existing-wall-3970042