Speaking to fijivillage Sports, Nasau says any major change to one of Fiji's biggest school sporting competitions should first be discussed with school heads and trialled before being implemented.
He says schools should have been given the opportunity to understand how the proposal would work, raise concerns and provide feedback before a final decision was made.
Nasau believes the new rule could strengthen some teams, but questions whether it will benefit school rugby in the long term.
He says allowing schools to bring in players who were not part of the team throughout the season could take away the passion, identity and sense of belonging that school rugby is built on.
Insert:Principal on new rule
Nasau says schools invest years developing players through the junior grades, making it unfair if those players lose their place to someone brought in just before the quarter-finals.
He says while new recruits may improve a team's chances on the field, they may struggle to fit into the culture, discipline and bond built by players who have trained together throughout the season.
Nasau also says the revised competition format has created additional costs and logistical challenges, with schools that qualify early now having to wait for the elimination matches to be completed instead of using that time to rest and prepare for the quarter-finals.
He says although Fiji Secondary Schools Rugby is assisting with logistics, schools are still responsible for meeting a number of other expenses.
Nasau says Queen Victoria School will respect the new rules this season but hopes Fiji Secondary Schools Rugby and school heads will review the changes once the competition concludes.
He also stresses that strict checks must be carried out to ensure any player joining a team under the new rule is a genuine student, saying the integrity of the Deans competition must be protected because the players are students first before they are rugby players.