git reword without resolving merge conflicts again

Is it possible to change commit messages using git rebase, but without having to re-resolve merge conflicts?

I need to bowdlerize an older repo and I don't want to change any of the actual code, just the messages.

I've tried --preserve-merges.

There's a little-known feature of git called "Reuse Recorded Resolutions", or rerere.

You can enable it globally by running git config --global rerere.enabled true.

If rerere is enabled, git will automatically save conflict resolutions, and will reuse those resolutions later if it encounters the same conflicts. This has the net result of not requiring the user to re-resolve these previously seen conflicts.

The feature is explained here - Git - Rerere.

The documentation for git rerere command is here - git-rerere(1).

Note: since The contrib/rerere-train.sh script is supposed to re-train rerere (you can see a manual retraining here)

To make sure rerere forgets all its current rebase resolution, you now have an official option with Git 2.14.x/2.15 (Q3 2017) for contrib/rerere-train: the --overwrite flag.

See commit ad53bf7 (26 Jul 2017) by Raman Gupta (rocketraman).
^{(Merged by Junio C Hamano -- gitster -- in commit aec68c3, 11 Aug 2017)}

contrib/rerere-train: optionally overwrite existing resolutions

Provide the user an option to overwrite existing resolutions using an --overwrite flag.

This might be used, for example, if the user knows that they already have an entry in their rerere cache for a conflict, but wish to drop it and retrain based on the merge commit(s) passed to the rerere-train script.