"change the III7 to a IM9(3rd in bass), "
Don't get this. III7 and IM9 are two different chords. Likewise, the real problem.
In writing any notation III7 is dominant. A seventh chord.
IM9 is a major 7 with a natural 9. A very common mistake in street writing. When paying big bucks to top notch session players, this mistake is not a good idea. You'll lose, regardless of your logic, and especially, your money.