Is there anything I can do to adjust the size of a stainless steel base ring, to make it slightly tighter? I’ve tried a smaller ring and it’s too tight. I would like to modify this one if possible. Thank you.
That is a very common problem, especially with off the shelf designs. Most guys need some sort of adjustment, including me. But most options aren't suitable for longer wear. Hope you find something that works for you.
I have opened up several stainless steel ( and nickel plated) cock / ball trap rings by using a drum sander (120 grit) and a 20v electric drill. Just take your time and run the drum sander around the inside of the ring until you are good with the size. Hand polish with 200, 400, and 600 grit sand paper and you will be happy. The current ball trap base ring that I wear started and 2.00” and is now 2.035” . Opening it up 0.035 and creating a flat inside the ring has made it almost perfect. So starting with a smaller ring is easier.....shrinking rings.....not so easy...
You could try adding some silicone tubing around the whole ring, this would reduce the size slightly, you could try tape, but I think any type of tape would cause skin irritation. The one exception to this might be the white plumbers ptfe tape.