What is the ruling on replacing the word "عبده" (His servant) with "عبدك" (Your servant) in the last tashahhud?

Two forms of the Tashahhud have been authentically reported from the Prophet (peace be upon him): The first is from Ibn Mas'ud (may Allah be pleased with him): "I bear witness that there is no god but Allah, and I bear witness that Muhammad is His slave and His Messenger." This is the most famous and soundest, and it is acted upon by the majority of scholars. The second is from Ibn Abbas (may Allah be pleased with them both): "I bear witness that there is no god but Allah, and I bear witness that Muhammad is the Messenger of Allah." It is not permissible to use forms other than these that have been reported from the Prophet (peace be upon him) in the Tashahhud. There is no need to make up past prayers in which something else was said out of ignorance.