I am trying to wrap my head around what you are asking here...
If you modify your package to change the resort, then you won't "lose" your tickets, and your park pass reservations will remain intact.
However, modifying is always subject to availability of the original package you booked at the new resort. If a package was a special offer that is not available any more, or is available but not for the specific room/resort you are rebooking to, you can't modify and would have to cancel and book a new package with new package terms. For example, if you had the package with "get two days free" on the tickets, and that offer is not available for the room type you want at the new resort, you would not be able to modify because when you got to "modify" it would show that room at the new resort as unavailable (even though it may still be available under a different package offer or room only). In that case, there is no way to just remove the "room" portion and keep your package tickets with the 2 days free as standalone tickets--you either modify the package to an available room with the original r at a new resort, or cancel and rebook, which removes the old tickets and gives you new ones at the new package price.
If this is overcomplicating things, just ignore me.