Is there a way to amend a commit without vi (or your $EDITOR) popping up with the option to modify your commit message, but simply reusing the prev
vi
$EDITOR
Since git 1.7.9 version you can also use git commit --amend --no-edit to get your result.
git commit --amend --no-edit
Note that this will not include metadata from the other commit such as the timestamp which may or may not be important to you.