Locksmith allows you to set messages at different scopes. It is possible to set the messages up for individual passcode or newsletter key conditions which can allow for greater flexibility. When present, a key-condition-level message will always override messages set up at the lock-level.
If you are having issues with your lock message being overridden, this can easily be fixed by clicking on the key condition and deleting the message inside of the key condition popup under "Custom input prompt". After you delete it, you should see a greyed out version of the message you've set at the lock-level, which means you're good to go: