Yes you can. I've done it many times. The gel polish underneath would be dry and i'm assuming it would have been capped with the gel top coat, which would act as a base coat for the normal polish. read more
And in terms of removal, yes, it will be easier to take off and less damaging to your nails because it's just regular nail polish on top of the natural nail, and you won't need to soak them in pure acetone (which is extremely drying). read more
Use the foil and cotton ball method to remove your polish or dip in 100% pure acetone nail polish remover for several minutes. Make sure your regular nail polish is 100% dry before applying gel or it will not last as long as expected (2 weeks). read more