Find text and redefine font family name, style, size and leading.

Everything is not so simple and reliable there. In general, it is impossible to correctly change the properties of the text (depends on the text)

Try this

var s = activeDocument.activeLayer.textItem.contents;

var x1 = s.indexOf("consectetur");
if (x1 >= 0) set_text_style(x1, "consectetur".length, mdf); 
 

function mdf(d) 
    {
    try { 
        var sz_v = d.getUnitDoubleValue(stringIDToTypeID("impliedFontSize"));
        var sz_t = d.getUnitDoubleType(stringIDToTypeID("impliedFontSize"));
        d.putUnitDouble(stringIDToTypeID("impliedFontSize"), sz_t, sz_v+2);


        var sz_v = d.getUnitDoubleValue(stringIDToTypeID("impliedLeading"));
        var sz_t = d.getUnitDoubleType(stringIDToTypeID("impliedLeading"));
        d.putUnitDouble(stringIDToTypeID("impliedLeading"), sz_t, sz_v+2);
        }
    catch (e) { throw (e); }
    }

function set_text_style(from, len, style_modifier) 
    { 
    try { 
        // get textKey descriptor for activeLayer

        var r = new ActionReference(); 
        r.putEnumerated(stringIDToTypeID("textLayer"), stringIDToTypeID("ordinal"), stringIDToTypeID("targetEnum")); 
        var textKey = executeActionGet(r).getObjectValue(stringIDToTypeID("textKey"));

        var list = textKey.getList(stringIDToTypeID("textStyleRange"));
        var new_list = new ActionList(); 

        // get styles of each char, modify if needed
        var styles = new Array();           

        var x = 0; // chars counter

        for (var i = 0; i < list.count; i++)
            {
            var d = list.getObjectValue(i);

            var x0 = d.getInteger(stringIDToTypeID("from"));
            var x1 = d.getInteger(stringIDToTypeID("to"));

            var st = d.getObjectValue(stringIDToTypeID("textStyle"));

            for (var n = 0; n < x1-x0; n++)
                {
                if (x >= from && x < from+len) // modify current style
                    {
                    var d = new ActionDescriptor(); 
                    d.fromStream(st.toStream()); // duplicate style
                    style_modifier(d);           // modify current style
                    styles.push(d);
                    }
                else
                    {
                    styles.push(st);
                    }

                ++x;
                }
            }

        styles.push(new ActionDescriptor());

        // scan styles, modify if needed, compact to range (from-to)

        var from = 0;

        for (var i = 0; i < styles.length-1; i++)
            {
            if (!styles[i].isEqual(styles[i+1]))
                {
                var d = new ActionDescriptor(); 
                d.putInteger(stringIDToTypeID("from"), from); 
                d.putInteger(stringIDToTypeID("to"), i+1); 
                d.putObject(stringIDToTypeID("textStyle"), stringIDToTypeID("textStyle"), styles[i]); 

                new_list.putObject(stringIDToTypeID("textStyleRange"), d);

                from = i+1;
                }
            }

        // put new styles to textKey descriptor

        textKey.putList(stringIDToTypeID("textStyleRange"), new_list); 

        // set modified textKey back to textLayer

        var d = new ActionDescriptor(); 
        var r = new ActionReference(); 
        r.putEnumerated(stringIDToTypeID("textLayer"), stringIDToTypeID("ordinal"), stringIDToTypeID("targetEnum")); 
        d.putReference(stringIDToTypeID("null"), r); 
        d.putObject(stringIDToTypeID("to"), stringIDToTypeID("textLayer"), textKey); 

        executeAction(stringIDToTypeID("set"), d, DialogModes.NO); 
        } 

    catch (e) { alert(e); }  
    }