
If nail polish does in fact seal stickers well in general and you like its finish then I can't see any reason not to use it on your MBP.
However, there's always a risk of the polish's chemicals interacting poorly with your MBPs finish and potentially its heat. So to safeguard against these I would maybe try a really small spot on the bottom of your MBP and see how it goes after a week or so. If it turns out your MBP doesn't like polish then you've only ruined a small spot on the bottom.