65:23 One may pay more on a dowry in the following manner: If a person promised a dowry for his daughter, he may arrange with her fiancé that for each year the money remains with him the father will increase the amount by a certain sum. This is permitted because it’s merely like increasing her dowry; it is comparable to the father saying, “I will give you a present of a certain amount on this date and if I don't deliver it on that day, I will add such and such amount to it.” This arrangement must be agreed upon at the time they write the tanaim (the pre-wedding contract) because until that point the father has not yet committed anything, making this arrangement a single commitment. However, if when the tanaim were written, the father pledged a certain dowry with no conditions, he may not later change the arrangement to pay a larger sum at a later date.
65:24 If a Jew borrowed from a non-Jew with interest and another Jew co-signs the loan, they may agree that the non-Jewish lender may only demand payment initially from the borrower, turning to the co-signer only if the borrower defaults. They may not arrange for the non-Jewish lender to seek payment initially from the co-signer because that makes it as if the co-signer borrowed from the non-Jewish lender and lent it to the Jewish borrower. Similarly, if a non-Jew borrowed from a Jew with interest and another Jew is the co-signer, they may arrange that the Jewish lender may only seek payment initially from the non-Jewish borrower, only seeking payment from the co-signer if the borrower defaults. The Jewish lender may not stipulate that he can seek payment initially from the co-signer because that makes the co-signer like a borrower. However, if a Jewish co-signer only guarantees the principal and not the interest, one may arrange to collect it from him even initially.