Users have the ability to change the system to set default rate tables so that new matters/clients will default to a new set of rates. Old matters/clients can also remain on the old default rate tables.
Default rate tables can be set in System Settings > Rate Tables > New Default Rates
Additionally, when creating new rate tables, if a non-default table is created, there is a new button that says Make Default, which is located near the Save Name button.
Clicking the Make Default button brings up a dialog with options for how to handle older matters/clients that were on the default rate table.