Rex Hospital switched last month to new electronic medical records software, a technology shift so complex it will take about a month to complete and is being scripted like a full-scale emergency: 1,000 technical specialists, two round-the-clock command centers, daily strategy sessions and a vacation blackout for most employees. Durham-based Duke University Health System has already made a similar switch, and WakeMed Health & Hospitals plans to introduce the same software at its main campus in February. An integrated IT system coordinates all hospital departments, imaging labs and doctors offices on a single network for patient records and for generating bills.