I am not sure what you mean by “ESA module” could you please clarify?
You are right that there is no option to change the output impedance because it is not switchable like the input impedance is. Moku:Pro’s output impedance is 50 ohms and the setting you are seeing in the standalone waveform generator is the expected load of the DUT. Changing between the expected 50 ohm DUT and 1 Mohm DUT switches between the 0 dB gain (1 Vpp mode) and +14 dB gain (10 Vpp mode) on the output.
In Multi-instrument Mode, we removed this option in the WG slot instrument because the output could be going to either another instrument slot (which has a max of 1 Vpp) OR to the Moku:Pro output (which you can set to be either 0 dB gain or +14 dB gain). I hope this clears up the confusion between the two different implementations and if you have any other questions please let me know!