As posted by the original author:

Alright guys,

I found a way to solve our Esc key limitation!
It was actually quite simple once I figured out how to go about it. But without any proper documentation the figuring out part wasn't exactly easy.

A little explanation:

The new version checks for triggered keyboard shortcuts via the event listener system. I haven't found a way to make completely new and unused keyboard shortcuts, so I had to use preexisting ones. This meant however, it had to be a shortcut, which triggered an action that wasn't too intrusive. If I'd chosen the shortcut for the encyclopedia for example, then everytime we'd activated the mod the encyclopedia would have popped up too.

But I think I found the perfect ones:
They are called 'Save camera bookmark 1' and 'Save camera bookmark 2' and can be found under
Options > Control > Keyboard > Universal. They are by default set to Shift+F9 and Shift+F10, but can be freely configured by the player, which is pretty much exactly what I've been looking for.
Triggering will still save the camera bookmarks, but you won't notice it. I think this function is used more on the campaign map than in battles, but should anyone use it, there are still 10 bookmark slots available and the shortcuts could be configured accordingly.

The keyboard shortcuts are 'Save camera bookmark 1-4' (by default these are set to Shift + F9/F10/F11/F12) and 'Save camera bookmark 5' which has no default setting.

Shift+F9 (or whatever your setting) will now go through the modes just like before.
Shift+F10 (or whatever your setting) will now enable Spectator Mode.
Shift+F11 (or whatever your setting) will now enable Lord Mode.
Shift+F12 (or whatever your setting) will now enable Reinforcement Mode.
the unbound 'Save camera bookmark 5' shortcut (will have to be bound first) will now turn the AI control off.

This should make the usage of the mod a little bit more comfortable.

Cheers!