Modify message with an Outlook web add-in (when reading email, not composing)

Question

I'm trying to establish if this is even possible:

Can an outlook web add-in (i.e. a JavaScript add-in that works on the web and in outlook, not a COM based add-in) modify the body of an email while in read mode (i.e. the user is reading an email, not composing a new email or replying to an email).

What I need to do is trigger the add-in if the email contains hyperlinks (looks like I can do that with a contextual add-in using a regular expression) and then modify those hyperlinks (change the href or add an onClick event handler) so if the user clicks them the behaviour is different.

Answer 1

Based on @OutlookAdd-insTeam-MSFT comment I'll post my own answer:

You cannot modify the body of an email in read mode.

:(