What can we extrapolate from "Lema'an Lo Yelamdu eschem ... "?
Rashi and Ramban #1 (on Pasuk 11, citing the Sifri): This implies that in the event that they do Teshuvah and convert - even the seven nations - (to accept the seven Mitzvos B'nei No'ach - Ramban), one is permitted to accept them. 1
Ramban #2 (citing Rashi in Sotah, 35b): Teshuvah is only acceptable with regard to the other nations, but not to the seven nations.
See Sifsei Chachamim.
Why does the Torah add the phrase "Vechatasem la'Hashem Elokeichem"?