Is the prayer valid of one who has ruled by other than what Allah has revealed and then admitted and acknowledged that after years, and can a believer diminish any of the Beautiful Names of Allah, such as the Name "The Judge," for example?

The ruling on one who judges by other than what Allah has revealed differs between major disbelief (kufr akbar) and minor disbelief (kufr asghar). For one whose disbelief is major, his prayer or worship is not valid due to the loss of the condition of faith, as Allah Almighty says: "And whoever disbelieves in faith—his work has become worthless, and in the Hereafter he will be among the losers." If he repents, his prayer and worship become valid. As for one whose disbelief is minor, it does not affect the validity of his prayer if it meets the conditions and pillars. Repentance from any sin is accepted by Allah.