puppet specialization

gistfile1.pp

module/foo/manifests/init.pp:
class foo {
  file { 'foo':
    source => 'puppet:///modules/foo/usual-case.conf'
  }
}

module/foo/manifests/special.pp:
class foo::special inherits foo {
  File['foo'] {
    source => 'pupppet:///modules/foo/special-case.conf',
  }
}

manifests/site.pp:
node basenode {
  include foo
}

node special-foo inherits basenode {
  include foo::special
}