You can't take actions in the present which will alter the nature of the past.
"Ille qui nos omnes servabit"
So through a combination of circumstances John was able to advise Frank to think about following a different alternative path in time.
Big deal! I enjoyed the trip.
Unless it's possible to communicate to the past or future with a device such as that radio, except much more advanced that breaks the laws of physics. I don't think physical transfer of human body to future or past is possible, but something like contacting or sending a message, may be possible, and if not, who gives a crap.
The increase in human knowledge is the cause of the decline of religions.