When changing coils on factory preset machines, Tesoro recomends that you send the machine back into the factory so they can tune the coil and machine to optimum performance. Factory preset GB machines are balanced to the coils at the factory so if you change coils later on it may not be at optimum performance. Will it work? Of course, you may not even notice any difference, but you could also be loosing performance. If you have two standard coils that you always use and switch off between, you can send the machine back in with coils, and they will pick the optimum setting so both coils work at the best possible performance. Dont get me wrong, you will not loose tons of depth, but it wont be at optimum performance.
This problem does not exist with manualy GB Tesoro machines, you can switch coils as often as you like. The GB process automatically acccounts for the balance of machine to coil and soil. This is one of the other benefits of having a manually GB's machine over a factory preset machine that most people dont realize.