In a 3-qt. slow cooker, combine chicken, dressing mix and wing sauce. Cook, covered, on low until chicken is tender, 3-4 hours.
Preheat oven to 425°. Shred chicken with two forks; stir in butter.
With one corner of an egg roll wrapper facing you, place 3 tablespoons chicken mixture just below center of wrapper; top with 1 teaspoon each feta and mozzarella cheeses. (Cover remaining wrappers with a damp paper towel until ready to use.) Fold bottom corner over filling; moisten remaining wrapper edges with water. Fold side corners toward center over filling; roll up tightly, pressing at the tip to seal. Place on parchment-lined baking sheets, seam side down. Repeat.
Bake until golden brown, 15-20 minutes. Let stand 5 minutes before serving.
In a large bowl, combine sausage and cottage cheese. Stuff into uncooked manicotti shells. Place in a greased 13×9-in. baking dish. Top with marinara sauce.
Cover and bake at 350° for 55-60 minutes or until a thermometer inserted into the center of a shell reads 160°.
Uncover; sprinkle with mozzarella cheese. Bake 8-10 minutes longer or until cheese is melted. Let stand for 5 minutes before serving. Freeze option: Transfer individual portions of cooled manicotti to freezer containers; freeze. To use, partially thaw in refrigerator overnight. Transfer to a microwave-safe dish and microwave on high, stirring occasionally and adding a little spaghetti sauce if necessary.