Do wet feathers change anything? Sure.
Does it affect accuracy? Sure. Does it matter? Maybe. If you have tuned your bow to shoot tail high the added weight of the feathers will bring your nock end down and make it fly straighter. A plus. It will impact higher but most people in the rain shoot lower because they are heavier. If you shoot with a shaft that comes out straight out of the bow you'll most likely still be fine although you may shoot to high., but then again your bow will most likely shoot slower so you will be fine as well. Does it effect things? I'd say yes. Is the effect negative? Maybe. Does a hunter need to know how the elements will effect his game? Most definitely. Don't wait to find out.