A Short Tribute

Reuben dedicated his property [for the public fund], and his widow now claims [the sum of] her ketuba [marriage contract]. This means that it is to be paid from the monies that her late husband designated for the hekdesh, since he had no other property. We seek that you instruct us, whether the law is on her side - since it is clearly stated in her ketuba that he issued a lien to her for land and additional property - or whether she does not have the authority to withdraw funds from the hekdesh…
The words of the scribes are rigorous and good, as those who have the authority to expropriate monies. Even if their rulings may be contested, it is usually appropriate to not to seize [funds] from their possession. Townspeople's amendments, however, are made according to the ways of merchants, through negotiation and as each generation sees fit, just as in our case, where they refrain from consuming designated properties, so as to maintain order and so that individuals not incur losses and the like, certainly no individual has the authority to annul a ruling [Din Torah] by contesting its amendment, the principal of law being is but general custom…According to the sum of reasons and explanations I have here written, it seems that the widow should be granted the power of attorney that the amount of her ketuba be paid out from the monies her late husband designated to the Hekdesh.

The custom to refrain from eating meat from the 17th of Tammuz is the equivalent of a vow. However, if one has the opportunity to participate in an obligatory festive meal they are permitted to eat meat, for it is not actually a vow but is considered as having accepted to undertake a fast. It is like saying "I will fulfill this commandment" when it is obligatory by law. Any case of a mitzvah is permitted, since a vow to fulfill a mitzvah is not applied at the expense of another mitzvah.