$ rm -rf a

  $ hg init a

  $ cd a

  $ echo a > a

  $ hg ci -Am0

  adding a

  $ hg tag t1 # 1

  $ hg tag --remove t1 # 2

  $ hg co 1

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg tag -r0 t1

  $ hg tags

  tip                                3:a49829c4fc11

  t1                                 0:f7b1eb17ad24