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

nadger
 /nad'jr/, v.

    [UK, from rude slang noun nadgers for testicles; compare American & British
    bollixed] Of software or hardware (not people), to twiddle some object in a
    hidden manner, generally so that it conforms better to some format. For
    instance, string printing routines on 8-bit processors often take the
    string text from the instruction stream, thus a print call looks like jsr
    print:"Hello world". The print routine has to nadger the saved instruction
    pointer so that the processor doesn't try to execute the text as
    instructions when the subroutine returns. See adger.


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

nadger

    /nad'jr/ [Great Britain] To modify software or hardware
   in a hidden manner, generally so that it conforms better to some
   format.

   For instance, an assembly code string printing subroutine
   that takes its string argument from the instruction stream would
   be called like this:

   	jsr print:"Hello world"

   The print routine would use the saved instruction pointer (its
   return address) to find its argument and would have to "nadger" it
   so that the processor returns to the instruction after the string.

   [Jargon File]

   (2014-07-09)