Sam, if you hold Techumin is a De’oraysa what would be the stress that he kept everything incuding that? The Maharal did keep the Girsa of Eiruvei Tavshilin, with a beautiful explanation of why this was picked.
Yibum might be a good example. There was a concept of Yibum which existed before matan Torah; that’s what Yehudah marrying Tamar was about. After matan Torah, the issur of marrying a daughter-in-law doesn’t allow this type of “Yibum”.
The ??????? in ????? the beginning of the Eleventh perek discuss this.
(Torah613Torah- response to earlier post: bereshis 24:63 and (ethics from sinai Irving Bunim-foot note says themidrash understands this description of “dwelling in tents” as the academies of shem and ever, Tanchuma, Toldos 2 and Va’yishlach 9)