I was curious if there were examples or instances where one generation of Rabbis established an interpretation of the law which was followed accordingly, only to have another generation of Rabbis lawfully reverse the previous decision entirely.
In Berachot 23a the Sanhedrin ruled that tefillin must not be brought in a bathroom. So people would leave them outside. But they frequently got stolen. So the Sanhedrin reversed its ruling.
Tevilas Ezra is one that comes to mind.
Avoda Zara 35b says:
ואלו דברים של עובדי כוכבים אסורין ואין איסורן איסור הנאה חלב שחלבו עובד כוכבים ואין ישראל רואהו והפת והשמן שלהן. רבי ובית דינו התירו השמן
there was a Decree not to drink/eat milk that a Goy milked without being seen by a Jew, and not to eat Bread and oil of the Goyim. Rebbi (Rabbi Yehuda Nesia see Rashi) and his Beis din permitted the oil made by a Goy (even though it was initially forbidden to eat).
One example that comes to mind is in Gittin 58b:
אמרו הלוקח מן הסיקריקון נותן לבעלים רביע ויד בעלים על העליונה רצו בקרקע נוטלין רצו במעות נוטלין אימתי בזמן שאין בידן ליקח אבל יש בידן ליקח הן קודמין לכל אדם רבי הושיב ב"ד ונמנו שאם שהתה בפני סיקריקון שנים עשר חודש כל הקודם ליקח זכה
Originally, Someone who buys land from a crimelord who stole the land from a fellow Jew by threat of death, should pay a quater (Ravs opinion) to the original owner and gets to keep the land. This only applies when the original owner cannot afford to buy his land back. If he can afford the original owner has first rights for the rest of time to buy his land back.
Rebbi made a new Beis Din convention that decided to change the law that the original owner has 12 months to repurchase his land, subsequently he loses his rights and anyone can buy the land and he gives the original owner a quater of the value.