no you can't overwind them. if it is automatic, there is a mechanism that stops you from overwinding and if it is manual it won't allow you to wind further once it is fully wound.
as far as the power reserve complication, it is more of a display of how much power is left, similar to the indicator in your car that tells you how much gas you have left.
as an aside, if it is automatic, then you don't need to wind it very much at all. once you get it going, you can slap it on your wrist and the natural movements that you make will get it wound.