Beitza 19a - Tevillas Keilim Bein Hashmashos

Rashi writes that you can't be tovel a kli during bein hashmashos because it is "not for a yom tov need". Maharsha asks, why doesn't rashi just say that it is assur bec. of all the 4 reasons mentioned earlier i.e. nir'ah kimisaken? He explains that it is going according to the opinion that during Bein Hashmashos all shevus is permitted, so he has to explain the issur is tevilla for a non-yom tov use, since it needs he'rev shemesh. It seems from the maharsha that the issur rashi refers to is not nir'ah kimsaken, but rather an issur to prepare on yom tov for afterwards. It should follow from the Maharsha that anytime you need the kli on shabbos you can be tovel it during bein hashmashos. The problem with this approach is that it seems to be against the halacha bec. we pasken like the mishnah in 2nd perek of shabbos (shulchan aruch 261:1), that you cannot be tovel keilim during bein hashmashos even if you will use them on shabbos.

I would like to suggest a slightly different peshat in rashi:

The m.b. (261) brings from magen avrohom (s.k. 6) that the mishna (and shulchan aruch 261:1) which says you cannot be tovel keilim during bein hashmashos is only speaking about a case where you have other keilim for shabbos, but if you need this kli bec. you don't have others, you can be tovel it during bein hashmashos (we pasken that they were not gozer on shevus only if it is absolutely necessary). Perhaps this is what rashi means. We are assuming that he needs this kli and has no others (that is why he is running to be tovel it during bein hashmashos). So, if this tevilla during bein hashmashos would be usable on yom tov, it would be permitted, but since it needs he'rev shemesh and is not usable for yom tov, therfore it is assur to be tovel it. The reason for the issur is not bec. of preparing for after yom tov, but rather that we are gozer on shevus that are not needed during bein hashmashos, so the issur is in fact bec. of nir'ah kimisaken.