I had this same question, and I figured it out on accident. For some reason the setting is not in the Radeon ReLive settings (from what I could find), but actually hidden in the toolbar.
First open the toolbar (default is Alt+Z)
You will see the toolbar overlay pop up, click the settings (gear icon)
In the middle you will see a square with a clock in it. Every time you click it it will cycle through all 4 corners, and then off as the last option.
Hope this helps
I have almost the same question with corection "is it possible to turn Overlay panel off to have alt_r no any action?"