In QS you can't assign actions to object, neither set up triggers for initial field selection. So, for initial selection, you can select value/values within that field and make sure they are selected when you save/close your QS document. In my case, I had an app that showed two filters with selections locked when opening it up.
Set analysis expressions, on the other hand, are not really meant for initial field selection. It is more about aggregation over a group of information independent of your current selections.