tweak

tweak vt.  1. To change slightly, usually in reference to a
   value.  Also used synonymously with {twiddle}.  If a program is
   almost correct, rather than figure out the precise problem you
   might just keep tweaking it until it works.  See {frobnicate}
   and {fudge factor}; also see {shotgun debugging}.  2. To
   {tune} or {bum} a program; preferred usage in the U.K.