Git se fusiona con el mensaje
$ git merge other-branch -m "Commit Message"
Lively Ladybird
$ git merge other-branch -m "Commit Message"press "i" (i for insert)
write your merge message.
press "esc" (escape)
write ":wq" (write & quit)
then press enter.
For current Git versions (2020+), just do git rebase -i -r <parent>,
then replace in the editor merge -C with merge -c.
This will open the merge commit's message in the editor during rebasing,
where you can change it