U.S. officials want to tinker with the mix of chemicals fueling missiles and rockets to gain an advantage in the Pacific by increasing the range of its front line munitions so U.S. forces can operate further away from China. The Pentagon and Congress are looking at a retrofit that could extend ranges for some current weapons as much as 20% by using more powerful propellants and lighter warheads, two congressional aides and two U.S. officials said who spoke to Reuters under the condition of anonymity because they were not authorized to speak publicly. Last week, the Senate revealed bill language…