The main challenge these day at LHR is getting from the departures level to the arrivals level to exit the terminal.

It was possible previously to go through a one-way door from the departures level to the arrivals level without assistance so a passenger can exit on their own. You know have to be escorted and securing an escort is not easy.

It is probably a lot easier rolling your ticket (i.e. changing to a new date) rather than cancelling the ticket. You do have to off-loaded the flight you were checked in on; can be done by phone or at the customer service desk.

It is possible and has happened for genuine reasons as a one-off but cannot imagine who would want to do this on a regular basis for any sane reason.