I've shortened many sets of manton rods. You won't get the end out. The way shorten them is put them in the lathe. Grind a cut off tools thickness to the amount you want to shorten them. Run the cut off into the rod just under the insert. The insert is hard so when you hit it, no big deal. Usually harder than the tool you'll use. So you wind up with the thickness of your cutter removed from the length of the rod, and the insert bare in that spot. Then heat a little and press the insert deeper into the rod.

manton reams that press fit, and you'll keep your rod straight this way.