Ostensibly,
XSetWindowStyle(XGetWindow(GetDlgItem(Dlg%hWnd, ID)))
However, I don't think it will work at all. Most control styles are settable only on creation, and subsequent change is ignored, or even misbehaves (XSetWindowStyle calls SetWindowLong). You can try it though.
For LBS_MULTIPLESEL, there should be a relatively easy workaround (keep it activated, but handle selection change and retain only the last selected item). For LVS_NOSORTHEADER, define your own CTL_COLUMNCLICK callback which does nothing -- it does not remove the arrow though.
