Can a blended family agreement address what a stepparent may or may not discipline a child for?

Yes, a parenting agreement or informal family understanding can set out expectations about a stepparent's role in discipline, even though there's no legal requirement to do so - this is a common source of blended-family friction, and many parents find it helpful to agree in advance on things like which decisions remain with the biological parent, what day-to-day corrections a stepparent can reasonably make, and what topics are off-limits for the stepparent to weigh in on without the biological parent present.

Ultimately, discipline within a household during a parent's own parenting time is largely left to that parent's judgment, including decisions about what role a new partner plays, and a family court generally won't dictate the details of household discipline unless it rises to an actual best-interests concern, such as conduct that's harmful or excessive. So an agreement like this functions mainly as a private understanding between the adults to reduce friction and provide clarity to the stepparent and child, rather than a legally binding or court-enforceable rulebook. If discipline disagreements are causing real tension in your blended family, a family counsellor or mediator experienced with blended families can often help more than a formal legal document.