Let me make sure I am understanding your question correctly...you are asking if you make room only reservations and then a package comes out, can you change your reservations?
You can always change your reservations, granted you can't get the same reservations if you get a package, say if your room only reservations are in a different type room than your package. I don't see why you don't think you can't change your reservations, you can!
Am I on the right track...?