Have you tried a more simple approach? perhaps you can call in to a Customer Service Agent and ask for the following.
Phone Number 1 - Plan A.
You: Hello CSR, Can you change my price plan to this <Plan B> Plan?
Phone Number 2 - Plan B
You: Hello CSR, Can you change my price plan to this <Plan A> Plan?
I believe this is what your goal was, correct? There is no need for a TOR or a Port in this case.
Just as long as the plans are still currently offered in-market plans then sure this can be done, otherwise Retentions may need to get involved.
I put the "HO" back in "HOFO"