You can use an environment filter to change the author of commits. Just modify and export
$GIT_AUTHOR_NAME in the script to change who authored the commit.
Create a file
filter.sh with contents like so:
if [ "$GIT_AUTHOR_NAME" = "Author to Change From" ] then export GIT_AUTHOR_NAME="Author to Change To" export GIT_AUTHOR_EMAIL="email@example.com" fi
filter-branch from the command line:
chmod +x ./filter.sh git filter-branch --env-filter ./filter.sh