I would have no problem using other planets OUTSIDE of our solar system for that, but aren't you placing all of your eggs in one basket trying that with earth?: 'To infinity or bust.'
If you observe the locations of the current planets in our system, even slight changes in their placement would bring annihilation. Jupiter alone 'rescues' us from a barrage of planet killing asteroids on a regular basis. A slight movement on our polar axis would cause us to either burn up or freeze. We would need to keep our tilt perfectly in place and our proximity to the sun exactly the same or risk turning into a 'dead' planet.
Why not just start with a currently 'dead' planet. If things go well, we can propel it using the same technology we developed to reach it, (which doesn't exist yet). Using current tech, the nearest candidate is roughly 40,000 years away. Obviously, that won't do, unless you are very patient. Even then, the tech that arrives couldn't possibly be used to propel a planet anywhere. Maybe we could 'practice' on a planetoid like Pluto, learning to adjust its orbit and tilt and terraform until it is more inhabitable, but we would still be taking a terrible chance since it is a planet killer itself and is close enough to earth to be a threat if we somehow screw up.
It sounds to me like some serious 'exponential leaps' need to occur before we could even consider 'detaching' a planet from its orbit and using it as a spacecraft.