amendum
An addendum (an added statement at the end of a document) that is at the same time and amendment (a change to a document. More specifically something added at the end of an email or text that fixes or clarifies an earlier statement.
Rob: Michael is a twat.
Mike: No I'm not
Rob: I'm just kidding. Please except my amendum... Michael is a huge twat.
Mike: No I'm not
Rob: I'm just kidding. Please except my amendum... Michael is a huge twat.