Since you have the wings glued together already, I would just leave it. Its very hard cut wings apart without making a pretty good mess after they have already been glued. For modifiying dihedral before the wings are glued is pretty simple. I found that most of the dihedral joiner pieces aren't all that tight a fit. It doesn't take much of a bigger gap at the middle to get an extra inch lower hihedral. I have only had to sand 1 joiner a bit to get the extra dihedral I needed. The rest of the joiner plates that came with the kits didn't need to be modified. I put a weight on the left side of the wing to keep it flat on the freezer(I mean work table) and a balsa piece to hold the I make a balsa piece to hold the right side of the wing at the right height for the dihedral. Glue together with 2 hr. epoxy. When it drys you will have a tight fit at the bottom of the wing and a slight gap at the top. If there is a big gap, say 1/8" or bigger I get scrap balsa, coat it in epoxy and fill the gap with that. When it drys, I fill any tiny gap that is left with epoxy. If the gap is small to start with, just fill it up with epoxy. Finish by getting a 4" wide strip of fiberglass and use thinned epoxy or Medium CA to glue it down over the centre so that 2" is on each side of the joint. If you use Ca, use a piece of wax paper under your finger to pat the CA into the fiberglass. Sand smooth when its dry before covering. I have had some pretty hard crashes and have never had a wing come apart yet.