$ \textbf{echo third change >> myfile}
$ \textbf{hg commit -m 'third change'}
$ \textbf{hg backout --merge -m 'back out second change' 1}
reverting myfile
created new head
changeset  backs out changeset 
merging with changeset 
merging myfile
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)