I’ve drawn the space of a hinge on a box design.
It took me a while and now it would be nice to copy and rotate this “hole” to the other corner of the box. (I know I would also need to change the direction of pushes/pulls after I placed it on its new spot.)
(Not to mention that I forgot to make the component unique before modifying it and now it has a hinge space on the opposite corner as well 
.)
Any idea?
Copy the geometry of the mortise out of the components and paste in place outside then complete the volume by filling in the missing edge. Or, if the components are solids, draw a box volume in place over the mortise and use the components and the Solid Tools to trim it to shape.
Make the front piece unique and edit it to remove that geometry.
BTW, you should be flipping the components to make the counterparts instead of rotating them end for end.
FWIW, I would have modeled the hinge mortise volume and used it to cut the box parts using Eneroth Solid Tools or Bool Tools 2. Here with Trim and Subtract from Eneroth Solid Tools. I modeled the volume of the mortise so it could cut the mortises in the top in the same process although I didn’t bother modeling the parts for the top.
