It might be worth asking our friends in the British Army how they grew accustomed to training for vastly different operational scenarios from the late 1960s until the mid-1990s. During that period it had battalions conducting counterterrorist operations in Northern Ireland as well as having forces prepared for conventional warfare in Germany. Although counterterrorism isn't the same thing as counterinsurgency, the Bloody Sunday episode taught the COIN lesson of not gratuitously offending a major part of the local population. The British experience appears to have some similarity to what the U.S. is facing today.