People joined the Israelites in Egypt during the night of the Exodus?

Question

I noticed something strange in Shemot 12:43-50. I always assumed the commandments given there were for future generations (like most commentators teach). But then it says in verse 43: "And HaShem said to Moshe and Aharon.." followed by 47: "all the congregation of Israel shall keep it" and in verse 50 "thus did all the children of Israel, as HaShem commanded Moshe and Aharon".

Does this mean that at that moment in Egypt other people could join? I find this strange, but then again a mixed multitude went with them (verse 38).

(P.s. Rashi - according to the Sefaria website - teaches that this chapter was spoken to them on the 14th day of Nisan)

Answer 1

In the sefer Ahavat Chaim by Chacham Menachem Menashe ztz"l, it brings down that there were other "low-Class" people that weren't accepted by Egyptian society at that time. They felt they were "like" the Jews and stuck to them. So when it came time for the Jews to leave, these people(aptly called the "erev rav") also joined the Jewish people since they identified with them, to some extent. Although I don't recall there being explicit permission for them to join.

Answer 2

If I understand your question correctly, you are asking if the rules of the Korban Pesach (listed in Shemos 12:43-50) were kept by the Jews that first year in Egypt.

If so, this is addressed by Shadal to 12:50, who says that they kept all of these rules in the first Pesach, in Egypt. He notes that Ibn Ezra there disagrees and understands that this verse is referring to the first Pesach in the desert, but not the one in Egypt (based on the concept of "Ein Mukdam Umeuchar").