There seems to be no easy way to make have conflicting shortcuts and explictly control which shortcut takes precedence under what circumstances.

E.g.

I want CTRL-R to mean something in this widget but something else all the rest of the time.

Related to this request is QWidget::grabShortCut() see:
http://doc.qtsoftware.com/4.5/qwidget.html#grabShortcut

If QAction had an activatedAmbigously() signal and this signal was emitted every time the conflicting shortcut was invoked it be relatively easy to just connect activatedAmbigously() to activated() on the actions one would want to take priority.