Remap ESC to Option-ESC in Office (Excel, Word, etc) with karabiner-elements
If I understand your question correctly, you'd like to have ⌥ Option Esc function like that of remapped Safari's Esc key.

In Karabiner Elements, you have to modify the JSON  file and remove the entry making it for Safari only:

You have to remove the following section:

{
              "type": "frontmost_application_if",
              "bundle_identifiers": [
                "^com.apple.Safari"
              ]
            }


Karabiner-Elements has a number of examples that you can base new keys from.  It's also important that your read the manual on how the application functions.