Yes, as long as you are modifying your original is not released until the new one is confirmed. I’ve done this several times. Your modified res will have the same number as the original
this is exactly what i did. I changed my original one bedroom WL/CC Dec 10-18 to Dec 10-15
when i then changed to this Cabin one, i needed a CM’s help because it became 2 reservations - one night studio and 4 night cabin. But if it is just changing one, you will be fine