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

hand-hacking
 n.

    1. [rare] The practice of translating hot spots from an HLL into
    hand-tuned assembler, as opposed to trying to coerce the compiler into
    generating better code. Both the term and the practice are becoming
    uncommon. See tune, by hand; syn. with v. cruft.

    2. [common] More generally, manual construction or patching of data sets
    that would normally be generated by a translation utility and interpreted
    by another program, and aren't really designed to be read or modified by
    humans.