How do you change the keys inserted while holding the Option key? The Option key influences what characters are inserted when pressing different keys.

For example, Option-k is ˚ and Option-Shift-k is .

Is it possible to modify these? Is it possible to, for example, make Option-Space insert an En-space? And if so, how would I go about doing such a thing?
You can remap keys with Ukelele or Karabiner.

http://scripts.sil.org/ukelele

https://pqrs.org/osx/karabiner/