Load and select your pre-morphed figure. Now find the base Genesis in the content library and double-click it. You should be asked what you want to do - choose to apply it to the current figure, not to load a new one. Now hit Undo which will restore the lost posing and materials but will leave the new morphs loaded and ready for use. You could also save a Character preset (a DSF format preset, not one of the “deprecated” script-based presets) which would do the same thing without needing the undo step.
So I’ve done those things, I can see “Clothing” and the sliders—but when I move the sliders, nothing changes, either on the Genesis figure or on the clothing. Shouldn’t I be seeing something change? Should the change appear on the Genesis figure? Or just the clothing?