I'm a bit perplex why you've chosen to pedantize this particular word choice since "prepend" itself is a portmanteau derived by mashing "pre" and "append" together.

Perhaps the trio of "affix", "prefix" and "suffix" might be more useful, since there is no "postpend" or "suppend" to accompany "append" and "prepend".

Regardless, the Google ngram chart of these various words is pretty interesting: http://books.google.com/ngrams/graph?content=prepend%2Cappen...