When/IF you switched from a 30 amp to a 50 amp service there is a lot of things to be changed. To put it in basic terms, you are going from a 120 volt 30 amp input to a 240 volt 50 amp input. As mentioned, this means changing your complete input main breaker panel as well as all wiring leading up to it, including the transfer switch, etc.
It would be much easier to put the second AC on it's own circuit with it's own extension cord that could be plugged in to a separate 120 volt/20 amp outlet on the pedestal. Most RV park pedestals have two outlets and some have three. They are 50 amp, 30 amp, and 20 amp(which looks like a standard wall outlet.
This would mean that your 30 amp main breaker panel is only dealing with one AC unit and a completely separate circuit is taking care of AC number 2.