Once the user has selected from the drop down, that selection is stored so unless you have another ‘action’ that is overwriting this field for a future stage what they selected will still be visible to users throughout future stages.
From what you are asking I think you may have this situation. Are you for instance populating this drop down from a connect action? If so, refer to this post
You can though use the ‘set field’ script to set the selection item in a drop down where you can set the drop down to a specific item by using the VALUE for that selection. ie if in your case here ‘cat’ has the value of 2 for its item, set up the set field to the required drop down and then enter 2 into the ‘text or number’ field in the value property in the set field script
if this still isn’t helping, perhaps will be clearer if you can set up an example form to show what you want to do and send over to us via the support ticket