My promotion to SGT is going through an exception to policy due to the fault of my S1. Also I qualify for a bonus based on me being promoted.Is there also an exception to policy once my promotion is back dated - for me to get the bonus

Just bring the back dated promotion to your Career Counselor and they can submit an exception to policy through HRC.

Your Career Counselor may tell you to submit a DA Form 4187 through your chain of command. With the back of your chain, it should go through no problem.