Reneging FT MO Offer for SA FO Offer

So I was a SA at a BB in NYC as part of their finance program, meaning I would become a MO FT after graduation. I accepted the offer after the summer as it was my only offer at the time, and coming from a non-target, a good offer all things considered.

However, I interviewed and received an offer at another BB as a SA in a FO role. I would be extending my graduation for a semester to do this, and would have no guarantees since it is a SA position, but I am considering taking the risk. Thoughts?

Thanks