Re:Yevamos 6a: The "HECHSHER MITZVAH" in Honoring one's parents >From Rashi it seems that the acts of slaughtering and cooking are only Hechsher Mitsvah. One possibility of explanation is that the Tora never told the son to do slaughter or cook, so one cannot consider these acts Mitsvoth, therefore they must be only in the category of Hechsher Mitsvah. Alternately - or in addition - we can say that the request of the parent is actually only the creation of an opportunity to honor the parent, and the act iself is a vehicle for the Mitsvah, a Hechsher Mitsvah. The actual Mitsvah is "doing what the parent requested", and this Mitsvah can be fulfilled even by words alone, which we learn are not considered acts which confer culpability according to Rabbi Yohanan. In Kidushin 31a we read 'Tani Avimi Brei D'Rabbi Abahu: Yesh maachil l'Aviv Pasyoni v'tordo min haolam', and in Yoreh Deah 240D VeYitnenu Lo b'sever panim yafoth, sheafilu ma'achilo b'chol yom petumoth, v'herah lo panim zoafoth - ne'enash alav. Hence any act in itself is not the Kiyum of Kibud of the parents - the Kiyum is in the attitude, in the expression of love and honor, despite the fact that perhaps the food is a Heftsa of the mitzvah.
Rashi explains the term "Hechsher Mitzvah" here differently from the way it is used in all other places, and here it does not refer to an act that is only a means to performing the Mitzvah. Your explanation is elucidating Tosfos, who explains "Hechsher Mitzvah" here to mean an act that is only a means to performing the Mitzvah, and is not the act of the Mitzvah itself. Tosfos explains, though, that if one's father asks him to be Mechamer on Shabbos, it is not a "Hechsher Mitzvah" alone, but nevertheless the Gemara calls it a "Hechsher Mitzvah" because usually (based on "Rov") it is a "Hechsher Mitzvah," such as when one's father asks him to dress him, and the person must be Mechamer in order to bring the clothes to his father. (The Rishonim write similarly.)
Nonetheless, your logic is very good (the MESHECH CHACHMAH writes a similar logic in Parshas Shoftim with regard to the Mitzvah to listen to the king, and the Mitzvah to listen to the Chachamim). Indeed, the KEREN ORAH here says the same thing that you are suggesting (as well as Rav Aharon Yaffen in his footnotes to the Ritva, #313:3). The only question is how that explanation fits with the "Hechsher Mitzvah" mentioned in our Sugya with regard to Binyan Beis ha'Mikdash? (The Keren Orah says that there, too, the Mitzvah is not the act of building, but that there should be a resultant place that is built for the Shechinah. That explanation is difficult, because the verse clearly implies that the Mitzvah is the act of building the place, "v'Asu Li Mikdash.")
I am not at home with my seforim so I can not tell you what SIMON this is in. However the TERUMAS HADESHEN in Hilchos Chanuka has a TESHUVA concerning KOVSO ZOKUK LOH, if the candle goes out is one required to re-light the candle and in that TESHUVA he mentions this Gemmorah and his explanation of HECHSER MITZVA is: Although one does not fulfill the Mitzva of Kibbud Av UNTIl he feeds him. By slaughtering the animal TO prepare the father he is preparing for the Mitzvah and therefore he says a hechsher Mitzvah would (at this point of the Gemmorah) be as powerful as a mitzvah and the same rules of DICHUY would appply to a HECHSHER MITZVAH as to a Mitzvah itself.
I hope all is well with you.
The explanation of the TERUMAS HA'DESHEN is consistent with the explanation of TOSFOS. Tosfos, though, had a difficulty, that sometimes the act of cooking or leading an animal that one does for one's parent is in itself the fulfillment of the Mitzvah of Kibud Av, and it is not merely the means to fulfilling the Mitzvah, such as in a situation where one's father told his son specifically to cook for him (and not because he wants to eat the food). If so, how does the Gemara know that the act is only a Hechsher Mitzvah for Kibud Av? Therefore they answer that in most situations, it is only an act of Hechser Mitzvah.