When I wanted to see if I can change the key, I couldn't find it, because all the other key assignment settings are in "Window Manager" → "Keyboard" and "Keyboard" → "Application Shortcuts". This seems to be the only key assignment setting in "Window Manager Tweaks". I think it will be more discoverable in "Windows Manager" → "Keyboard".
Maybe there is no place for such a setting in Window Manager → Keyboard (currently only one of a few modifiers can be chosen), so I make the request more general.
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