You can now prioritise your rates: Rooms/Rates -> Occpuancy Rates. The lower the number, the higher priority it will have over any other rates which may cover the same date span/days.
So for example, rather than have to setup multiple start/end dates, just to accommodate a higher rate for the May holiday weekend, you can simply enter:
Rooms/Rates -> Check rates for errors - will not show a duplicate rate, as ID56541 has a higher priority than the default ID49693.
Please let me know if this isn't clear.