I have not been able to find a way to load tax rates in CE 1.9 that are effective from a future date, or to enter increase/decrease in tax rate at a future date. There appear to be no tax validity periods anywhere. Can anyone help please.
That functionality does not exist, you would need to build a custom module to do this. Tax rates don't normally require frequent automated changes (to my knowledge!).
How many tax rates do you have that are going to change? How often do these tax rates change? Do they all change at the same time? Could you export your current tax rates (Sales > Tax > Import / Export) and have them ready to upload on the change date?