When I worked as a tech at HRO in Salem, one of my jobs was opening up transceivers for "MARS" mods. The one requirement was that they had to have a MARS license. Back then (in the late 80's and early 90's), the knowledge was kept pretty close to the vest. Eventually a publishing company called ARTSCII came out with whole books on how to do the mods...My job became less doing the mods and more repairing the botched jobs that came in. Some were so bad that the damage incurred rendered the handheld irrepairable. If the botched job was on an HF transceiver, the job was somewhat easier and probably worth the repair. I think I saw more botched jobs on HF transceivers because...CB. They also got the radio back with only the transmit enabled on the ham bands again...and a very large bill.