Kahr never made a "K9 Covert". I do not think you will find anyone that has cut down a K9, doing so would weaken the frame and remove a steel from around the magwell.
I had a K40 Covert that developed a crack in the frame in the rear of the magwell. I asked Kahr if it was repairable, their response was no and they replaced it with a MK40 because the K40 Covert was discontinued years before.
The thread you listed shows a K40 Covert not a K9 Covert. In fact if you look closely at the picture you posted, you can see the K40 on the slide.
P40 Covert/ FN High Power in 40
Pair of Ruger Vaquero Bisleys 45LC
S&W 610 / Taurus 817UL 38 Special +P
Colt Pocket 1903 32 ACP / KelTec P32
SASS Member / NRA Member / Kahr Club # 22