Yes, just like any other clothing item, you can also alter these sets as per your needs. Even after careful consideration and endless searches, you often end up purchasing a pyjama top and bottoms that do not fit your right. Well, in such cases it is best to alter them. Of course, you can do that! You can either do it by yourself if you are an expert tailor or hand them over to someone who does the job better than you. Also, in either case, make sure that the seams and stitches after the alteration is strong enough and will not wear out quickly.