Thank everyone for the suggestions. I will double check with international
student officers. ISO officers from 3 different universities told me that I
can do CPT or OPT with another program, but two of them didn't say whether
it is a higher level or not. One said this when I asked him about getting
enrolled into a master program at statistical department. He knew at that
time that I had my PhD.
Maybe, there are ways to get around.If I find out,I will post it and let
everyone know.