Holding Alt to Box deselect is a common option in DCC apps. We engine edited it into the code path, but it would be nice to get official support. Thanks!
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Steps to Reproduce
Try to deselect actors using a box select.
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Hi Matt! One of the reasons we haven’t done this is because the default way to invoke the marquee selection outside of animation mode (and other similar modes) is by holding Ctrl+Alt. However, I will track this request. It’s still something that could be added when the binding doesn’t conflict.
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Hi
I’m not affiliated with Matt, I just happened to see this EPS ticket! 
Just wanted to mention that box deselection of rig controls in animation mode is also a very highly wished for feature of our unreal animators. In maya the hotkey happens to be CTRL+drag to box deselect.
Apologies for the interuption!
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Hi Luke! It’s good to get a boost on how desired this is.
When this is implemented, we will likely use Alt over Ctrl as Ctrl+Mouse drags are already used by the indirect interactions on the transform gizmo.
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Awesome, thank you! If you do submit it to UE Main let us know the CL so we can integrate it 
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