The last development release adds a new feature that had been in my mind for a while already. I have added a way to control which visiblity conditions are shown in the preview. Until now all visibility conditions were rendered as if their condition was true. Now if you click on the Visibility Condition State button (the eye next to the LOD selection) you can select which condition is true (and thus shown) and which one is false (and thus hidden).
The screenshot below shows how the control looks for the default Extra 300 of FSX. I have selected one of the three propeller states to be shown in the preview. This makes it easier to inspect how the model looks under these conditions.
Whatever selection you make for the preview has no impact on how the model is exported. All visibility conditions are always exported.