Just add the highlighted line to the function
Javascript code:
function SetIcon (hWnd, nStatus, bIsContactBlocked) {
var sIcon = MsgPlus.ScriptFilesPath + '\\' + oStatus[nStatus] + (bIsContactBlocked ? '_blocked' : '') + '.ico';
var hIcon = Interop.Call("shell32", "ExtractIconW", hWnd, sIcon, 0);
Interop.Call('user32', 'SendMessageW', hWnd, 0x80, 0, hIcon);
Interop.Call('user32', 'SendMessageW', hWnd, 0x80, 1, hIcon);}