I toyed with getting a stainless steel guiderod for my MK9 but after reading some of the stuff on the Kahr shop site about the possible need for trimmimg, adjusting diameter of the new rod decided I would leave my well functioning gun alone. the site shows the muzzle end of the new rod as screwing in, I took my MK9 apart this AM and tried to manipulate both the muzzle and breech end of the spring to see if i could get them to unscrew, but when they would not come easily and would not come with some rubber under a pair of needle nose pliers I abandoned further attempts for fear of marring these parts.
If no one else responds the next thing to do would be t o call or email the folks at Kahr, and when you find out let us know, and if you get the assembly let us know if it just fitted right in or had to be worked on.
shoot safely and well!