You are going to fuel a large debate with this. When the smoke and dust clears it comes down to this...... It is not recommended, but yes you can because it is your tank.
However, it is done and there are plenty of experienced reefers with yellow tangs in smaller tanks. The main thing is that your are willing to take it to a LFS and exchange it for store credit (if they allow it) when it grows too large.
But there are more issues that just that. What it comes down to is if the fish is healthy and not stressed. You may or may not be able to tell depending on your reefing skills.
I think if you could ask reefers and promise not to tell you would find many more have yellow tangs in their tanks than will admit on a forum to avoid a debate and being lectured to by the "tang police". Many are concerned about the health of a fish that needs large amounts of room to swim and behave in a natural way, and with good reasons. For these reasons it is not recommended.
Do your research and make your own decision.