How much beer was dispensed? The issue is not going to be over carbonation but how much degassing took place. Possibly you could reconstitute the gas in the beer once the beer came down to temperature (38F). You probably should apply 14 PSIG and roll the keg every once and a while to try to evenly distribute the gas. No guarantees with this practice.
As to if the beer was over-carbonated, shaking the excess gas down is not the best practice if you want to re-obtain the specified gas content. You will risk flat beer if you over shake. The beer may pour clear but will not be very palatable.
Scott Zuhse, Instructor
Micro Matic Dispense Institute