This is done by first ensuring that autosave is off. Then, exit Legacy mode without saving. When you now load your legacy again your popularity will have been restored and you have not and will not be challenged again.
To do this start a new legacy and win the tourney. Then go to 'Punch Totals' in the last fight and press B and you will get +5 added to your Power, Stamina, and Heart. You can keep repeating this until your stats are at maximum.