I am curious why you would want to do that. Tinkering with the internals of a GPS is something I, as an electronic technician, would not be thinking of doing.
Perhaps you have the same problem I had when using the GPS in the car, plugged in to the cig lighter socket, and it turns itself off every time you stop the engine.
I simply wired a second, permanently connected to battery (via a fuse), cig lighter socket to the dash board. This gets exclusively used by the GPS.
Problem solved and no mods to the GPS required.
Klaus