That depends on your definition of easily. The shaft is rotated by a centrifugal advancer located on the clutch side of the engine. The advancer is preloaded with a spring. You can rotate the shaft but you should feel some resistance as you overcome the tension applied by the spring. If the shaft moves freely without any resistance then chances are good it’s damaged/snapped. To get an idea of how the KIPS system works check out the JustKDX home page, click on tech tips then the KIPS article.
Be sure that when you reinstall the advancer you're careful to properly position its shaft on each end. It’s possible to correctly fit the case side of the shaft but misalign the clutch side so the shaft doesn't fit in the clutch cover properly. If the shaft in not properly installed then either the clutch side engine cover will split as you tighten it down or once the engine is fired up.
While you have the clutch cover off to check the shaft take a second to inspect the water pump shaft to ensure its still in good condition where it rides against the outer water pump shaft seal and unless seal has recently been replaced now would be a good time to do it. Also check the seal on top the clutch actuating arm where it comes out of the clutch cover and the shaft were the seal rides against. If the seal is in poor condition replace it, same with the shaft. When this seal starts to go bad water from either a water crossing or just washing the bike can get into the transmission.
I hope that helps,
David