A little bit of luck is needed. I've upgraded the tuners for two of my guitars without problem. Then I wanted to upgrade the tuners on my Squier Telecaster: The small holes for the pins on the underside were in the wrong place. I thought, ok, let's drill new holes. Unfortunately I needed to drill the new holes right beside the old holes; which meant that my drill kept slipping into the old hole and I don't have the necessary equipment to fix everything, so those shiny expensive tuners are still waiting for their day.