As far as I know,it can not be custom.You can change the type like these:
function onDataBound(e) {
var colorArr = ["#FF0000", "#FF8C00", "#006400", "#40E0D0", "#800080"];
var iconShapeArr = ["triangle", "square", "triangle", "cross"];
var chart = e.sender;
var series = chart.options.series;
for(var index = 0; index <= series.length - 1; index++) {
chart.options.series[index].color = colorArr[index];
chart.options.series[index].markers.background = colorArr[index];
chart.options.series[index].markers.type = iconShapeArr[index];
}
}