I'm pretty sure that by returning your car to "stock" you will unmarry the tuner from the vehicle. I also believe there is a limited number of times you can marry it to other vehicles...5 I think. Now, returning the same car to stock and back to tuned again does not count as a complete unmarry....only when the strategy code/ECU/VIN changes.
Also, remember to switch out your 3 bar for the stock 2 bar BEFORE loading it back to stock to be safe.