Lonewolf, you needed to put it in a higher gear than first in order to loosen the nut, otherwise yes, that will turn the engine over.

 

If using a breaker bar yes...but i don't know many people who have impact guns...whether they be electric or air...that will use a breaker bar

 

Undo the nut before you pull the chain and you won't need to pop it in gear at all. The weight of the bike will keep anything from spinning. If you have an impact gun it will pop off with the bike on the stand with little trouble.