Using frozen peaches instead of fresh peaches

Sure you can use frozen peaches. Once peach season is gone, I use either frozen or canned peaches myself. You will want to thaw and drain them well, though. Then add in the extra tablespoon of flour it suggests for extra juicy peaches. One other hint, which I use to bump up the flavor- add a 1/2 teaspoon of almond extract to your peach slices and toss them in it a bit to coat. Then layer them into the crust as usual. The extract helps give them a little accented flavor to bring out the peachy. It can give you a slightly pinkish tinge as well, so don't get alarmed. It's a "peachy" pink, so it won't look out of place at all.