“A change would do you good,” according to that noted management consultant, Sheryl Crow. But for the U.S. Postal Service, change has been wrenching,  particularly when it means shaking the habits acquired during years as a complacent semi-monopoly. A couple of recent reports highlight the rigors of reinvention for USPS leaders, not just in chasing new revenue and overhauling slipshod management practices, but in ultimately retooling their sprawling operation to survive in the digital age. You might think, for example, that the Postal Service enjoys an inside track with its sister agencies in the federal government. Instead, it’s taking a beating from private-sector rivals in competing for a big part of agencies’ shipping…