Given a commit history that looks somewhat like
A---B---C---D master
\ \
S---T---U---V feature
I need to reword all commits of the feature branch, leaving all other commits unchanged. The result should be
A---B---C---D master
\ \
S'--T'--U'--V' feature
If I only had to reword commits since the last merge of master into feature, I would usually do an interactive rebase from V. If I try to do an interactive rebase from S, it also includes the commits C and D, which I do not want to change at all.
Beyond the above example for visualization, the master branch was updated with thousands of commits since the initial feature commit, merged into feature around a dozen times, and feature also has ~500 commits, none of which have been merged into master so far. The commit message changes will have to be performed manually, not just e.g. adding a prefix to each commit.