If you have any gunsmith experience, they are easy to replace. Take the old one out with an easy out, measure how long the one you took out is and file the new one to be the same length. The hole should be counter sunk just a hair. I put anti seize on mine, I screw them in and tighten them with plyers but don't torque them down. Cut off the stub about 1/16" above the barrel, be really careful and don't get your saw into the barrel, I did once, yuck. Peen around the edges of what stub is left to get the liner into the countersink and make it invisible when you file it off flush with the barrel.
A good job should look like this, I had some that showed a partial line around them because my countersink was wonky.
View attachment 279248