You can actually influence what appears in COMMIT_EDITMSG before you even start typing.
If you close the COMMIT_EDITMSG file without adding any text (or if you delete the existing text), Git will abort the commit, assuming you changed your mind [5.5]. COMMIT-EDITMSG
Understanding .git/COMMIT_EDITMSG : The Heart of Meaningful History You can actually influence what appears in COMMIT_EDITMSG