Q: How do I change the upcoming year's rates, without affecting this past years rates?
The best (safest) way is to duplicate each rate that's changing, and set the Season Dates of each one appropriately. This way you have one set of rates for 2005 and another set for 2006. This is better than just changing the old rate definitions because it will keep an auto-calculation from affecting old reservations, particularly long-term stays.
In Rates Setup, select each rate definition that will change (you can use Ctrl-click to select many at once), and click "Copy Selected Rates". Now edit each rate definition -- in each of the old rates, put the old range like "1/1/05 to 12/31/05" in the Season Dates Applicable field. In each of the new rates, put "1/1/06 to 12/31/06" (and change the charge amount and descriptions, of course).