The gemara suggests that according to Rav Meir it would be forbidden to put on two pair of tefillin on Shabbos even though one is not intending to fulfill a mitzvah and even though there is no mitzvah of tefillin on Shabbos, because R. Meir holds that one can be in violation of ba'al tosif even not in the time of the mitzvah, even without kavana to be yotzei. The gemara challenges this assumption - ועוד הישן בשמיני בסוכה ילקה. Meaning, if it is indeed true that one can be in violation of bal tosif even after the mitzvah is done, even without intending to fulfill the mitzvah, one should receive malkus for sleeping in the succah on the night of shemini atzeres (in eretz yisroel). It is not clear what source the gemara is asking this question from. Perhaps that is true that according to Rav Meir one would receive malkus for sleeping in a succah the night after succos? Rashi explains that the question of the gemara is coming from the minhag in chutz la'aretz to sleep in the succah on שמיני ספק שביעי, the night of shemini atzeres. How can we sleep in the succah on shemini atzeres night and not be concerned for violating bal tosif? Rashi explains that the answer must be that since we are only intending to fulfill the mitzvah of the tzad that it is still succos (and not yet shemini atzeres), the intent helps to avoid bal tosif. Therefore, according to Rashi, the gemara is saying that we cannot explain that according to Rav Meir one violates bal tosif after the time of the mitzvah, even without intent, because if that were true, we couldn't sleep in the succah on shemini atzeres.
In my sefer Nasiach B'chukecha (page 277) I asked a question on this sugya. Based on Tosafos in Succah 39a and other rishonim who hold that if one explicitly intends NOT to be yotzei, they are not yotzei, perhaps the reason we can sleep in the succah on the night of shemini atzeres is because our intent is that if it is not succos anymore we are intending NOT to be yotzei, thereby avoiding bal tosif. Meaning, even if assume that Rav Meir holds that not intending wouldn't help to avoid bal tosif, intending NOT to be yotzei should avoid bal tosif? The Gaon Yakov asks this question. He explains that even if we accept that according to the opinion that מצות א"צ כוונה, intending NOT to be yotzei would allow one to not be yotzei the mitzvah, it wouldn't help to avoid bal tosif. He doesn't explain why there should be a distinction. However, it seems that the distinction is simple. The rationale as to why one doesn't fulfill a mitzvah when they explicitly intend not to is that we can't force people to fulfill mitzvos. If you don't want to fulfill a mitzvah, you aren't in fulfillment of that mitzvah. This rationale only helps to avoid the fulfilling of a mitzva, but would not help to avoid the violation of bal tosif.
However, the Gaon Yakov limits this sevara to the opinion who holds that to violate bal tosif שלא בזמנו לא בעי כוונה. Since not having intent to be yotzei doesn't avoid bal tosif, intending NOT to be yotzei may also not avoid bal tosif. But according to the conclusion of the gemara in Rosh Hashana that לעבור שלא בזמנו בעי כוונה, one only violates after the z'man when they have kavana to be yotzei the mitzvah, having kavana not to be yotzei should work even within the time frame of the mitzvah. Therefore, the Gaon Yakov paskens l'halacha that even within the time of the mitzvah one can avoid bal tosif by intending NOT to be yotzei. However, the Magen Avrohom (34:3) and Gr"a hold that intending not to be yotzei doesn't help at all to avoid the violation of bal tosif.