An added disorientation of the trip was doing Yomtov Sheini in Israel. While there are minyanim for outsiders for Pesach and Sukkos, there wasn't any for Shavuos in Givat Zev. As a chiyuv to say kaddish for my mother, this was unpleasant, but at least I could daven while they were davening and say kaddish.
If I was saying the Shemoneh Esrei of Yomtov, and the tzibbur was saying that of a weekday, was my davening tefilla betzibur? I would say yes. The first and last three brachos are the same, and the main thing is standing before Hashem and davening. What you're davening doesn't make any difference, as long as we're all saying Shemoneh Esrei. I am told that this is indeed the opinion of Rav Usher Weiss.
On the other hand, other rabbis, namely Reb Moshe Feinstein and Reb Shlomo Zalman Auerbach, hold that this is not called tefilla betzibur. With all due respect to Rabbi Usher Weiss, whose opinion is held in high regard by many people, and despite my high estimation of my own opinion, let's assume like Reb Moshe and Reb Shlomo Zalman.
So I was left saying Shemoneh Esrei without a minyan. Sure, I had Barchu and Kedusha and Kaddish, but I did not have tefilla betzibbur. This bothered me, because part of the kibbud Av of Aveilus is to daven betzibbur, not just to say kaddish.
So I came up with an idea. It is clear in OC 268 that the weekday Shemoneh Esrei is a valid option for Shabbos and Yomtov, but the Anshei Knesses HaGedola gave us a different nusach to make davening less burdensome. On that basis, the mechaber there paskens that if one forgot it was Shabbos/Yomtov, and began Attah Chonein instead of Attah Kidashta/Yismechu/Attach Echad/Attah vechartanu, he is obligated to finish Attach Chonein with a bracha, and only then return to the Shabbos/Yomtov Shemoneh Esrei. This extends even to the point that if you mistakenly said Barech Aleinu on Shabbos, and said Tal uMattar in the summer, you would have to repeat it. Strange, but true.
This is based on Brachos 21a:
אמר רב יהודה אמר שמואל היה עומד בתפילה ונזכר שהתפלל פוסק, ואפי' באמצע ברכה. איני והאמר רב נחמן כי הוינן בי רבה בר אבוה בען מיניה, הני בני בי רב דטעו ומדכרי דחול בשבת מהו שיגמרו, ואמר לן גומרין כל אותה ברכה. הכי השתא, התם גברא בר חיובא הוא ורבנן הוא דלא אטרחוהו משום כבוד שבת, אבל הכא הא צלי ליה
By doing so, I would be saying the same thing as the others there, and I would have Tefilla BeTzibur.
(I only made this proposal regarding Maariv, Shachris, and Mincha, but not Mussaf, because Mussaf has nothing to do with the regular weekday Shemoneh Esrei, as the Rambam says (10 Tefilla 7)
מי שטעה והתפלל של חול בשבת לא יצא. ואם נזכר והוא בתוך התפלה גומר ברכה שהתחיל בה וחוזר ומתפלל של שבת. במה דברים אמורים בערבית או בשחרית או במנחה. אבל במוסף פוסק אפילו באמצע הברכה
and the Kesef Mishna there explains
וסובר רבינו דכיון דבמוסף לא היה בדין לצלויי י"ח ....פוסק ואפילו באמצע ברכה)
Rav Horowitz said, and I quote, "זה חשבון טוב, אבל זה לא חשבון שלך." "It is a good analysis, but it is not your analysis to make." In other words, the logic is good. The halacha is correct. But I should not be fiddling with the nusach Chazal instituted.
Out of respect of the Rav, I only did this in one of the Shmoneh Esreis of the day, in Shacharis, and even then I only added Atta Chonein and Hashiveinu. I figured that Shavuos is the day of tefilla for Hatzlacha in Limud HaTorah (see Mahrsha RH 16a, and this article in Yeshurun,) so what better brachos are there than Daas and Torah? Then I switched back to Attah Bechartanu and finished the nusach for Yomtov. It was a "seven-plus-two" Shemoneh Esrei.
I kind of regret not doing this all the time. I think it's an excellent idea. I don't believe it would be called meshaneh mimatbei'ah, I don't believe it's like saying mezonos on an apple. If it were, then the mechaber in 268 would not say that you are obligated to finish the bracha. Also, it's Yomtov Sheinu in Israel, for goodness sakes! I'm not suggesting that this be done regularly, I saying that under the circumstances, it's a legitimate application of Chazal's intent. But Rav Horowitz definitely knows more than I do, he's a professional poseik and a yarei Shamyim, and I did, after all, ask him for a psak. Also, my personal interest may have colored my opinion (along the lines of "every man who is his own lawyer has a fool for a client," or "A Rebbe who is his own Chassid has a fool for a Rebbe.) I guess that listening to him was the right thing to do.
They bring down the Shelah (Maseches Shabbos #33) that says that if this mistake happens to a person, and he has to finish the weekday bracha, he should be nervous and upset the whole week. Someone suggested that this shows that it's not a good thing. I say, I'm no expert on the Shelah, but a raya it's not. The Shelah is talking about forgetting that it's Yomtov, an indifference which shows disrespect, a zilzul of the chag. I'm talking about intentionally adding to the tefilla with full awareness that it's yomtov and the intention to say the proper Shemoneh Esrei.
I have finally decided that this depends on a machlokes between the girsa and the shitta of the Sefer haManhig/Rashi in the Pardes/the Tanchuma, and the Ohr Zarua.
The Sefer haManhig (Shabbos 11) and the Abudraham (after Mincha of Shabbos) say that when the Gemara says pshat in לא אטרחוהו that it means that it's assur to ask for your need on Shabbos because you will come to be mitz'ta'eir.
Similarly, Sefer haPardes (p 315) says assur, and this is also found in the Shibalei HaLeket (128.)
The Tanchuma is in the beginning of Vayeira, where he talks about the problem of Meitzar, which contradicts oneg and menucha.
But I believe they had a different girsa in the Gemara, and I believe that our girsa is the basis of the Ohr Zarua (Krias Shma 95) who says clearly that even though there's an issur to be shoeil tzrachim on Shabbos, that does not apply when you're using the nusach of Shmoneh Esrei that was created by the Anshei KhG. His words:
אי לאו משום לא אטרחיה משון כבוד שבת היה נכון להתפלל כל י"ח