OK. I see your difference now and why you'd want to change that.
I guess first is how far along that edge is it out ?
A few inches or the entire run?
If it's just a few inches I'd carefully slice the edges and fold them up so I could trim the inside panel edge back the 5/16".
I think MP&C has a little tool he made up from a screwdriver or something that will open those up real slick like. If it's the whole edge...
If you have space, time, the tools and determination it can be done.
A less 'proper' way would be trim it where you want it and (using all the proper techniques for welding a panel) weld up the seem and finish it up that way.
The down side is on the next guy who has to change the skin.
