I have a 2009 macbook now running sierra on an SSD. It is great and works well, quite impressed. Now I am also getting a 2009 macbook pro in next week or two. What If I swapped the HDD? I think Sierra will error and crash. But is it conceivable that it might work? I will make a full time machine backup as I normally do first. Worth a try? AS I said I think the hardware ID will make it crash/error/etc.