If you got the references to both tweens, you could stop one and start the other
That said, why two separate animations! I find that a single one that is controlled via PlayForward/PlayBackwards is much much better, for these reasons:
1. If the second tween starts while the first one hasn't finished yet, it will still start from the beginning, so you'll see a "jump" to the end of the first tween, and then the backwards animation will start playing. Using the same tween/animation instead has no such issues.
2. An "out" ease is always nice when making something appear, while an "in" ease is nice when making stuff disappear, so the same tween played backwards will have exactly that effect
3. It's a single tween VS 2