The Jargon File (version 4.4.7, 29 Dec 2003):

munge
 /muhnj/, vt.

    1. [derogatory] To imperfectly transform information.

    2. A comprehensive rewrite of a routine, data structure or the whole
    program.

    3. To modify data in some way the speaker doesn't need to go into right now
    or cannot describe succinctly (compare mumble).

    4. To add spamblock to an email address.

    This term is often confused with mung, which probably was derived from
    it. However, it also appears the word munge was in common use in Scotland
    in the 1940s, and in Yorkshire in the 1950s, as a verb, meaning to munch up
    into a masticated mess, and as a noun, meaning the result of munging
    something up (the parallel with the kluge/kludge pair is amusing). The
    OED reports ?munge? as an archaic verb meaning ?to wipe (a person's nose)?.


The Free On-line Dictionary of Computing (30 December 2018):

munge

   /muhnj/ 1. A derogatory term meaning to imperfectly transform
   information.

   2. A comprehensive rewrite of a routine, data structure or the
   whole program.

   This term is often confused with mung and may derive from
   it, or possibly vice-versa.  One correspondent believes it
   derives from the french "mange" /monzh/, eat.

   [Jargon File]

   (2002-04-15)