If they are laced on it would be easy and you have plenty of choices. If they are sewn in then you’ll need a heavy duty sewing machine or split D-rings. I’ve never seen screw together D’s, ovals yes at West Marine. All I have ever seen is stainless D-rings, either formed or cut. I use light weight formed and welded D-rings on my travel BP&W, heavy cut D-rings on my cold water setup. Brass would look classy but probably be too soft.
This is why I like BP&W (Back Plate and Wings), you can change and add in minutes, I actually wish I had plastic D-rings for my light weight travel wing.