Can you start a sentence with Or?

You can if you would choose to, but not if you want to get a good grade or to be thought of with intelligence.

Yes, but it's not recommended.

Explanation:

Based on the experiences i have had with teachers, they don't seem to like the idea, as it doesn't sound very professional and academic. Try using synonyms like:

as a choice.

as a substitute.

as an alternative.

conversely.

either.

in other words.

in preference to.

in turn.