I wrote this little thing

doas -u _postgresql psql --dbname=maddy --host=localhost --username=maddy "UPDATE passwords SET value = '$(maddy hash --password "$1")' WHERE key = '$2' AND value = '$(maddy hash --password "$3")'"

First argument is the new password (hashed of course), the second being the username, the third being the old (current) password. I haven’t yet tried this but I might now.