That's possible. For any page foo, there is a corresponding file data/meta/foo.changes
that holds the history of that page.
The .changes files are TSV files where the username is the 5th field.
There may exist some other way I'm not aware of, but since your DW is running on Debian, you could type that kind of commands in a terminal. Warning, it's completely untested. You should backup your entire system and make sure you can actually restore the backup before you try this. Don't blindly type the commands, adapt to your situation, check for errors at each step.
sudo systemctl stop apache2
sudo su -s /bin/bash - www-data
for ch in $(find . -name '*.changes'); do
touch -r "$ch" reference.timestamp
sed -i -e $'s/^\\([^\t]*\t[^\t]*\t[^\t]*\t[^\t]*\t\\)'"$oldusername"$'\\(.*\\)/\\1'"$newusername"'\2/' "$ch"
touch -r reference.timestamp "$ch"
sudo systemctl start apache2