Based on this, the Sefer Harirai Kedem explains the abovementioned Gemara in Kiddushin. With the form of teshuvah, similar to that of Rosh Hashanah, a person becomes a tzaddik even though he has not done the mitzvah of teshuvah to remove his individual sins. Once he decides with conviction that he will abandon the wrong path and is determined to start following the right path, he attains the status of a tzaddik. Therefore, when the individual proposed kiddushin on condition that he is a tzaddik gamur, we can assume that perhaps he had this form of teshuvah in mind, namely to change direction – which does not require anything verbal and is not lengthy. Thus the kiddushin is valid, as he attained the status of a tzaddik even though he still has not atoned for his sins.
May we all be zocheh to fulfill the mitzvah of teshuvah in its entirety. Amen.