addendum vs modification

addendum

noun
  • A postscript. 

  • The height by which the tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line. 

  • Something to be added; especially text added as an appendix or supplement to a document. 

modification

noun
  • The result of modifying something; a new or changed form. 

  • A change to an organism as a result of its environment that is not transmissable to offspring. 

  • the change undergone by a word when used in a construction (for instance am => 'm in I'm) 

  • The act of making a change to something while keeping its essential character intact; an alteration or adjustment. 

  • a change to a word when it is borrowed by another language 

How often have the words addendum and modification occurred in a corpus of books? (source: Google Ngram Viewer )