How do I make a certain keyboard command system wide?
Keyboard Maestro is a very powerful and easy to use keyboard macro app. If you want a multi-step process available everywhere on your Mac you can't do much better.

By "multi-step process" I mean, to use your example, no matter what app I'm using right now, pressing a certain key combination performs these steps.


Quickly switch to the Wire Tap app.
Press CmdShiftT in the Wire Tap app.
Quickly switch back to whatever app you were previously in.


This all happens so quickly that you can barely tell any app switching occurred.

I use it to start and stop my time tracking app at the press of a keystroke, for instance, as well as ensuring that Cmd+ zooms in no matter what graphics app I'm using and Cmd- zooms out.