A: Yes, it does matter. Begin breaking in the new shoes during a few shorter runs and at least two long runs before running the marathon.
Of course, I'm assuming you choose the same brand of shoe you've been training in. If you're trying a new shoe brand, complete a dozen shorter runs in them before wearing them on a long run.
Be confident that the new style is right for you before you run too many miles. Also, do your long runs on the road since that's probably the surface you'll be running on in the marathon.
Shoes respond differently to various types of terrain, so you'll want to simulate race conditions during your long runs.
Remember, your running gait changes somewhat at the end of a long run, and your feet swell, too. Make sure your shoes have extra toe room, good cushioning, a snug fit in the arch and heel, and a stable base.
And don't forget to test the shoes with the socks and inserts you plan to wear on race day.