Ubiquitin, I think HaLeiVi answered your questions nicely, and it’s unfair to narrow it down to a yes or no question (as in, “Did you stop beating your wife? Yes or no!).
Before matan Torah, the mitzvos existed in a different form. They were all about the “spirutal achievement” (to coin a phrase which probably misses the point), not about the technical “kiyum ha mitzvah”.
That all changed after matan Torah, when we became m’tzuveh v’oseh, and the benefit of the mitzvah became bound to the technical performance of the mitzvah.
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”.
It’s possible that before matan Torah, the accomplishment of the mitzvah of Tefillin could be achieved without what we would consider to be kosher Tefillin, but after matan Torah, it would be a meaningless act.
Some mitzvos may have been tied to the limud of those inyanim, similar to our saying korbonos, tefilah b’mokom korbonos, saying the Avodah on Yom Kipur, etc., even today.
This approach could also explain Succah, but one can also say that the “l’maan yeidu” before matan Torah was a yediah of the future, and afterward, a yediah of the past.
It’s also worth noting that the z’manim of the year are bound to the events which occurred, but not necessarily in the way of cause and effect in which we normally think of them. We call Pesach “Z’man Cheiruseinu”, and we normaly assume that we commemorate the cheirus of yetzias Mtzrayim. Realy, it’s more than that. HKB”H created the world so that 15 Nisan is a z’man of cheirus, and therefoe, that’s when yetzias Mitzrayim took place (histakel b’Oraisa uvara alma). So too Z’man Simchaseinu, and Z’man Matan Toraseinu. It’s therefore possible for the avos, even before matan Torah, to have celebrated the moadim.