I'm not a fan of putting the truck into neutral for safety. You never know when you'll need to get on the gas to get out of a sudden situation. Under stress what seems like a routine, simple movement or action will often get missed or delayed....not to mention if you do put the truck back in gear, the transmission is always slow and lazy to react which does nothing but cause you precious time you may need to react one way or another.

In terms of manually shifting your transmission and harm. You'll get varied responses from most everywhere you look but I'd to lean more towards the no corner. There are too many electronic safeties and controls for enough harm to be done to the point it will negatively affect the life of the transmission.