I think you are missing the point of "completing a stay" which implies checking out, too much of a palaver for me for it to be so important to use a lounge anyway....but whatever floats your boat. It depends upon which hotel you are talking about but insisting on accessing a lounge is a little DYKWIA. If it really important to you, then mention in passing your impending change of status as part of a conversation and put it in the form of an enquiry as to how it works rather than ambush them with your knowledge of your understanding of the T&C's. ( But I am English)