Remap touch bar control keys, e.g., Siri I'd like to customize what the keys in my Macbook Pro's touch bar do. For instance, I have no interest in Siri but I'd be great to have the Siri key be the hotkey for iterm2 for instance.

Is there a way to customize the action for the "system" part of the touch bar's keys?
Whilst you can't completely customise the actions provided in the control strip, you can replace or remove buttons with other Apple-provided buttons. Go to System Preferences → Keyboard → Customise Control Strip… and replace the buttons on the Touch Bar with any other options.