Not that hard
Had some free time to work on it.
It wasn't all that bad.
Plastic one, under the sink, was harder of the two. Not much room to work. Plastic kept on grabbing the drill bit. Used a vibrating saw to cut a part of it. Wacked it a few times until it came loose. Screwed it out.
Brass one was easy. Hardest part was drilling the hole. Drilled four holes and used a jig saw to connect the holes. Made enough room for a sawzaw blade to fit and cut as close to the sides as I could. Chiseled out about 1/4 of the cap. Wacked it until it came loose and unscrewed it.
New ones went in with teflon tape and white grease.
Picture of old plugs.