Formerly Kerri Gowler, a change will see Williams vie against her younger sister for a spot in the four.
The single sculler will undertake a half-marathon fundraiser for cancer relief.
The Olympic silver medallists will combine in double sculls for Paris 2024.
The sculler admits the competitive itch needed to be scratched one last time.
The career switch comes after deciding commercial banking just wasn't his thing.
Dame Lisa Carrington and Aimee Fisher advanced overnight in Hungary.
The pair's contributions to their sport have seen them upgraded from members of the Order of Merit to companions.
Grace Prendergast and Kerri Williams (formerly Gowler) won pairs gold at Tokyo last year.
The Kiwi pair won by 2.26 seconds from Netherlands.
