The DexCool is a formula to protect the various metals used in the motor and the water pump. If you don't want the DexCool my recommendation would the Prestone that Mixes with any Color coolant. This is available at most auto parts stores, Walmart, Meijer, etc. The green has a different base to it and is not recommended by GM for the system.
The DexCool needs to be flushed out as much as you can to put in either, but with the Mixes with any color and Type product you don't need to be as careful. The green product is not compatible with DexCool, so you must flush and rinse out all DexCool.