How to modify existing, unpushed commit messages?

Answer 1

You can use git-rebase-reword

It is designed to edit any commit (not just last) same way as commit --amend

$ git rebase-reword 

It is named after the action on rebase interactive to amend a commit: "reword". See this post and man -section interactive mode-

Examples:

$ git rebase-reword b68f560
$ git rebase-reword HEAD^