It is fairly easy to heat the insert and remove it if you are careful not to overheat it. Screw a good sized point into the insert, like a 145 grain, finger tight. Apply the flame to the point for about 10 seconds, and then try to pull the insert out by clamping the point in a vise or something. Repeat the 10 second burns until the insert pulls out. DO NOT apply any heat directly to the insert or shaft. If you apply too much heat to the point, you will know it because strands of carbon will pull out with the insert, and that's the end of that shaft unless you can use a short shaft cut off below the burn.
I don't know of any way to get a glued in nock out without ruining the shaft, plus sometimes nocks break and then you have a problem if it is glued in. You can use a glued in nock insert, if one is available for your shaft, which allows you to replace nocks, but that is difficult to remove also.