Additional Shofar Blasts And בל תוסיף

Tosfos Rosh Hashana (16b) asks how we can blow an additional set of shofar blasts in order to לערבב השטן if it is a violation of בל תוסיף, adding on to the Bibical mitzvah?  Tosfos ends up answering that doing a mitzvah multiple times does not constitute בל תוסיף.  The simple understanding is that the Torah gives a minimal shiur to do the mitzvah but it is not the maximum that one should violate בל תוסיף for doing more.  The Rashba answers the question of Tosfos that since one is blowing to fulfill the takanah of Chazal that is not a violation of בל תוסיף.  The Achronim discuss is there a machlokes in the answers, does Tosfos not hold like the answer of the Rashba and visa versa or did they just give alternate answers.  

The Minchas Chinuch (454) says the Rashba must agree to the severah of Tosfos for וכי תעלה על הדעת דלהרשב"א אסור ליטול לולב או להניח תפילין כ"פ ביום או הרבה זיתים מצה וכדומה, how can it be that Rashba won't allow you to carry around a luluv or eat a lot of matzah?  He must agree to Tosfos.  One could argue that the Rashba holds that is not a proof for all those examples are cases where adding to the mtizvah is an additional kium mitzvah, every taking of the luluv, every eating of the matzah, the mitzvah of tefillin is to wear it all day but blowing more shofar blasts is no additional kium mitzvah and maybe that is בל תוסיף to add to the mitzvah.  

Other Achronim attack the other way, how can Tosfos not say like the Rashba, why is sitting in the Sukkah on Shemini Atzeret not a violation of בל תוסיף if Tosfos does not say doing an acting to fulfill the takkanah of Chazal is not in violation of בל תוסיף?  The Pney Yehoshua and Pri Migadim (Pesicha Kolleles volume 1 #38) both suggest Tosfos is agreement with the Rashba when the takkanah serves to alleviate a need, where there was some problem Chazal had to fix, but just to enact an additional blowing does not fit in the rubric of the license for takkanas and would be subject to בל תוסיף.  Rebbe Akiva Eger says that this is not so for Tosfos himself (28b) [on the same page where he repeats his yesod from 16b] says that sitting in the sukkah on Shemini Atzeret (to fulfill the takkanah derabbanan of ספיקא דיומא) would be a violation of בל תוסיף according to what the Gemarah entertains that בל תוסיף applies even outside the timeframe of the mitzvah even with out intent to fulfill a mitzvah.  In other words, Tosfos is saying that בל תוסיף does apply to a Rabbinic decree and it is not a violation merely because one is not intending to do a mitzvah; not like the Rashba?  

My great-grandfather suggests that the Tosfos there does not necessarily contradict the Rashba.  The point of the Rashba is that it is not בל תוסיף when one's intent is to fulfill the Rabbinic law, not to add to the mitzvah. Tosfos is talking in the opinion that one's intent doesn't matter, one violates בל תוסיף even without intent for a mitzvah so over there the words of the Rashba do not hold water and doing a Rabbinic law will be בל תוסיף.  However, according to the conclusion of the Gemarah that when violates בל תוסיף outside the timeframe of the mitzvah only with intent for a mitzvah, Tosfos will agree to the Rashba.  

If everyone is on the same page why did the Tosfos and the Rashba give two different answers?  My great-grandfather says that they are addressing two different forms of בל תוסיף.  Tosfos (16b) says that the additional shofar blows are considered in the timeframe of the mitzvah for one may be summoned to blow for a different tzibbur.  The בל תוסיף that one is violating is the בל תוסיף of adding to a mitzvah like adding a 5^th species to the 4 species taken on Sukkot.  For that form of בל תוסיף it doesn't help if your intent is to fulfill a Rabbinic decree, one is still changing the form of a mitzvah and will violate בל תוסיף.  Therefore, Tosfos needs to be מחדש doing the mitzvah many times is not בל תוסיף.  However, there is room to argue with Tosfos (as R.A.E. 16b does,) and say even though one may be called to blow for someone else, it is still not considered within the timeframe of the mitzvah for the one blowing the shofar already did his mitzvah and he is just being מוציא the new crowd.  The Rashba maybe held like that and he is not addressing the form of בל תוסיף of adding to the form of a mitzvah for the mitzvah is done.  The Rashba is addressing a different form of בל תוסיף and that is the Chazal adding another mitzvah to the Torah is also a violation of בל תוסיף and for that he answers a Rabbinic decree not given over a new mitzvah is not subject to בל תוסיף. 

(For further reading on the topic see Yarech L'moadim siman 16, ראש השנה – תקיעות דרבנן ואיסור בל תוסיף of Rav Asher Weiss, עשיית מצוות יותר מכשיעור ואיסור בל תוסיף by Rabbi Ehrman.)