The parts counter at my dealer said I could switch to it, but it's tough to get all the green out. I just leave the green, and change it myself since I trust my owners manual, and don't know how much 'backward' compatibility' testing they really do.
Not changing at the specific intervals is water pump damage because of loss of lubrication additives and internal corrosion due to coolant becoming acidic. This can seriously impact the radiators ability to remove heat, as well as the engine to transfer heat to the coolant. I might even create headgasket or issues with other seals.