In our Daf Yomi series we've finished the Yevamot tractate and started K'tubot. The K'tuba is the marriage contract, but in standard form the tractate starts not with its putative subject but with a nearby issue: on what day of the week is a marriage supposed to take place? The rabbis discuss back and forth, if it has to be Wednesday or perhaps Tuesday, and why not Monday... After a while the question is raised if they are authorized to change a rule that seems to have been laid down in the Divine scriptures of the Torah, and the flat answer is yes, they have that authority, end of discussion.
They then ramble off into a discussion about dealing with persecution, and if the rampaging Romans who can be expected to interfere with Jewish weddings if they always take place on the same day of the week intend to kidnap the bride or merely rape all the wedding guests, and how to dissuade brides from committing suicide. These, however, it must be noted, are not sufficient reasons to change the basic rules. It is permitted to move weddings because of Romans but as an ad hoc measure, that's all, since Romans come and go (after a few centuries). Given that the Roman Empire is ephemeral, you can't change divine rules because of it. You merely wait for it to pass. (K'tubot 2-3).