The basic problem is this: I have a mini keyboard I'm using for a Raspberry Pi project, and since there is only one shift, ctrl and alt key apiece, that means combinations on the left side of the keyboard like shift-A and ctrl-C are kind of awkward to pull off without dropping it.
My intended solution is to add a separate button to simulate a second shift key. With the RPi and some very basic electronics and programming experience, this is fairly simple in theory. At least for most keys. But since the shift key is kind of a "modifier" key...
The question is, do Operating Systems handle each keypress separately or is it the keyboard's job to send a capital A when the user pushes shift-A? Can I use a second input to simulate a shift key and then push the A key on the keyboard to have the Operating System print a capital A? A general answer is appreciated, but if it depends on the Operating System, the OS in question is Raspbian Stretch, based on Debian Stretch.