Escape button in keyboard shortcuts editor
Currently (in Ae version 15.1.0) it is impossible to assign a hotkey combination that contains Esc button.
There is no Escape key in left upper corner in displayed keyboard model, so you cannot drag some action to button (or button to some action).
When you try to create a new key binding and press Esc, then this Keyboard Shortcuts window will just close.
This bug has an easy workaround: Press "ctrl + alt + ;" to open settings, then press Reveal Preferences in Explorer, then go to aeks folder and edit Custom.txt manually.
To solve this bug Adobe can add Esc button to keyboard model (for every layout) or do not close window at esc button. The same behavior is in Pr.
But why would you want to use the ESC key in this way? It's not a bug - they've reserved ESC for... escaping from stuff.
You know what, it doesn't matter. You can do this using AutoHotKey if you really want to.