Change rowcallback after initialisation

I need to get my hands on existing datatable's fnRowCallback setting but everything I try seems to fail.

What have I tried:

var dt = $('#table').dataTable({
            "bRetrieve": true,
            "fnRowCallback" : function (nRow, aData, iDisplayIndex, iDisplayIndexFull)    {
             console.warn("working");
             }
        );

and

var dt = $('#table').dataTable({"bRetrieve": true});

dt.fnSettings().fnRowCallback = function (nRow, aData, iDisplayIndex, iDisplayIndexFull) {
        console.warn("working");
    }

No luck, but if I change

var dt = $('#table').dataTable({"bRetrieve": true});
dt.fnSettings().sAjaxSource = "invalid url";

I get an error so that one seems to work. Also if I do fnRowCallback in the original datatable initialisation it works, but that's not what I want.