Modifications were done to some LC during the course of the war. I remember reading a damn good series of Naval Books about RN & RAN ships, in those books it was made mention a few times about refits an such to cruiser's. 1 such refit to a light cruiser included KGuns.
Sadly I now no longer have the books anymore but I do recall the bits about refits to some ships because at the time I thought "DAMN" to myself
Also there were a lot of unoffical refits and trials of gear that never made it into main stream so as I said, it did happen. How often and to what particular ships I have no idea. I have been looking to find out again but so far no joy
As to USN, couldn't tell u didly and quite frankly dont care much about it either.