If I use BuildTargetOutputFolder to set a new URL
the change only takes effect after close/reopen
project. I susspect that CC target to not listen
for changes in BTOF.

It seems from the code that OutputRoots listen on
BuildOptions so changes made from may work ok:

public void propertyChange(PropertyChangeEvent e) {
    String n = e.getPropertyName();
    if (BuildOptions.PROP_OUTPUT_FOLDER.equals(n)) {
        setDelegates(new FileSet[] {
getRoots(resolver, unit, opts) });
    }
}