Sub::Override allows the programmer to simply name the sub to replace
and to supply a sub to replace it with.

  my $override = Sub::Override->new('Some::sub', sub {'new data'});

  # which is equivalent to:
  my $override = Sub::Override->new;
  $override->replace('Some::sub', sub { 'new data' });

WWW: http://search.cpan.org/dist/Sub-Override/