Will - this site has some useful information or you might get help on their forum GPS data

Ltd4all - You're not compelled to follow what the GPS says. LOL. If you ignore the instructions to go via the bridge and take an alternative route it should update as you go and still give useful guidance when you're back on track. I'm not familiar with garmin so don't know if what you ask is possible on that. On my Tomtom I've created a series of "standard departure" itinery files to which I append the relevant destination, and "standard arrivals" which I select as appropriate depending on the direction of the departure point.
If your garmin has the ability to store itineries they are much more useful than simply using "go to".