The answer is both yes and no, depending on what you mean by “allowed to transfer”. Students who are undecided can NOT just declare Eng and get in. That is different than the other undecided kids from, say, A&S, who are allowed to simply declare English or Psych, or any of the other majors in A&S.
Having said that, though, they can apply to transfer in. As Dean J said, however, the number of people trying to transfer in is much higher than the number of slots opening up from people leaving Eng. Because of that it is very hard to get in if you were not originally accepted as an Eng student.