Can these metal roofing panels be applied over existing 1/2" sheathing?

Yes but watch moister build up. I over hung min by a foot.

I've helped install this type of sheeting on a home before & we left a 2 inch overhang on the gabled sides with what I'm sure was aluminum trim similar to steel roofing. I would say trim edging should be used on any roofing project to ensure maximum durability and life. We had about a 1 inch overhang in certain places over the rafters, but with flashing it seems almost impenetrable.