We recently released a large update for Moku:Lab and it now uses the same API as the Moku:Go and Moku:Pro. You can find help on changing the output impedance with Python here.
If you are still using the legacy version (pymoku), then there is no way to change the output load. This is because in reality the output load is not actually being changed like the input load can. The Moku:Lab’s output impedance is always at 50 Ohms, however, the “output load” setting in the app you see is an expected output load as seen by the Moku, which will only change the scaling of the peak-to-peak amplitude. This means, in pymoku, you just need to set the appropriate scaling manually based on the expected output load.
There is a similar post about this when using Multi-instrument Mode here that may be helpful as well.