Don't be confused that this is a matter of "heavy" versus "light". It's a matter of them deciding that such a dividing line exists in the first place. I pay for UNLIMITED usage per month. Period. Dont tell me after the fact that I am a problem.
Now then. If you want to change your billing method, just f'ing do it!
Great use of power to get a "news" story out there for an internal company test though. Awesome marketing. Dont be confused.