Considering a lot of the NYPD straight up said they'd resign if he became mayor, I think he's got a pretty good chance of bringing change if he really wants to

The department is administered and governed by the police commissioner, who is appointed by the mayor to what is, nominally, a five year term.

Can Zohran fire the existing commissioner and replace him? Idk what the bureaucracy around that looks like. Entrenched power structures have a way of slow rolling executives thru don't like and ignoring rules they don't want to follow.

A lot of levers of power that worked for a Guliani or an Adams might suddenly stop working assuming Zohran can make it all the way through the general and into office.

The potential is there, but usually winning one election is not enough to actually achieve structural change such as stopping racist police actions.