I installed XS sights on my Kahr, it was tough to get the old ones off. I had to put my slide in a vise, and use a brass punch to remove the old ones.
the new sights went on just find. If I remember right Kahr sights only come off one way.
Installing night sites on my PM9 was no problem. My boyfriend did it for me and he said it was slightly more difficult than his USPc, but not too bad.
He did use a sight pusher though. He found it hard to justify the $130 for the sight pusher, but he's already used it on two different firearms and will be using it again in a few weeks (HK P30). He said the money was worth it just though because its so much easier and also relieves the stress and worry of potentially harming the slide or sights.
I recently changed the factory sights on my P380 to Trijicons. The Trijicons were .003" wider than the Kahr sights so filing was necessary.