Modify Command Behavior With Key Held Down

 From:  fcwilt
12080.1 
Hi,

Is it possible to alter the behavior of a command based on control/shift/alt being held down.

For example, could the line command use one of those keys to determine if the line is drawn in both directions from the starting point.

There is an checkbox that does this but it would be grand if control/shift/alt could achieve the same result

Thanks.

Frederick