Whilst it is not possible to assign a keyboard shortcut/hotkey to this option directly, many of Impact's tools will in fact allow you to toggle this behaviour by simply holding the shift key during usual operation. Look out for the tool-tip hint in the bottom left-hand corner of the Impact window when using a tool for notification of when this is applicable.
Impact 2023 (Dynamic Constraints Edition) release is available for download, bringing with it a host of new features. Available here.
