Currently I verify the player by a unique identifier that is given by the server. If you clear PlayerPrefs, you will be able to submit another score, now as a different player. I can understand why you would want to remove this, so I will consider adding this as a toggle option too in the next update.
Can you also explain why when I upload a new entry from the same player, on this app it shows that the usernames were replaced, but on the callback function, both the old entry and the new one exist, causing some problems in the UI, eg. your old highscore with your old username shows up, as well as your new highscore with your new username.
