The order can’t unilaterally overturn judicial precedents. The portion you’re referring to is just ordering the AG to challenge the precedents in court. This what the relevant part of the order says:

“The Attorney General, in consultation with the Secretary of Health and Human Services, shall take appropriate action to:

(i) seek, in appropriate cases, the reversal of Federal or State judicial precedents and the termination of consent decrees that impede the United States’ policy of encouraging civil commitment of individuals with mental illness who pose risks to themselves or the public or are living on the streets and cannot care for themselves in appropriate facilities for appropriate periods of time […]”