Is it necessary, for someone who pronounced the two testimonies (Shahadatayn) as a precautionary measure, then it became clear that he had fallen into disbelief (kufr), to repeat the pronunciation of the two testimonies and to repeat the prayers he performed after the precautionary pronunciation?

If a person repents from what he considered to be disbelief (kufr) and pronounces the two testimonies of faith (Shahadatayn), his repentance is valid. He is not required to renew it after coming to know the true nature of the matter, because he has done what he was commanded to do. Repentance erases what came before it, and "the one who repents from sin is like one who has no sin."