Most of it already had.
The linear aerospike engine and the metallic TPS were tested and ready to go, as was the composite lox tank. The only holdup was in the composite liquid hydrogen tanks. If a crew only vehicle were built, it would eliminate the need for a payload bay. Without the payload bay, the liquid hydrogen tanks could be redesigned into a simpler shape, thus making their manufacture much easier. Without the need to carry a large amount of cargo into orbit, the weight savings could allow the fuel tanks to be built out of more conventional materials if needed.