I have heard that matzoh produced specifically with the intention that it will not be used on pesach is not included in the prohibition of eating matzoh on erev pesach. This seems to be based upon the wording of the Shulchan Aruch that "matzoh that one can fulfill his obligation with may not be eaten the whole day." However, that was said by Tosafos to exclude matzoh ashirah, e.g. egg matzoh. Can anyone bring a source to extend the leniency to this case?
There are a few Rishonim (Meiri, Rabbeinu Manoach) who explicitly permit eating matzah on erev pesach if it was manufactured shelo lishmah. However, one can infer from other Rishonim (Tosafot, Rambam) that such matzah would still be included in the prohibition.
R. Shlomo Zalman Auerbach was also reported to be opposed, although it may be possible to draw a distinction within his viewpoint between matzot manufactured without any particular intention at all, and those made specifically not to be used as matzot mitzvah.
The mishnah in Pesachim
The starting point for our discussion is the mishnah on Pesachim 99b:
עֶרֶב פְּסָחִים סָמוּךְ לַמִּנְחָה לֹא יֹאכַל אָדָם עַד שֶׁתֶּחְשַׁךְ.
On the eve of Passover, adjacent to minḥa time, a person may not eat until dark.
Tosafot s.v. lo yochal inquire as to what precisely the misnah is forbidding one to eat at this time. After all, absent the ruling of the mishnah, one would not eat be able to eat chametz (which becomes forbidden after the fourth hour of the day), nor matzah (which the Yerushalmi forbids on erev pesach)?
Tosafot answer that the mishnah is forbidding matzah ashirah from mincha time, which would otherwise be permitted. It is not chametz, but also does not fall into the category of forbidden matzah on erev pesach, because one cannot use it to fulfill the mitzvah of matzah at the seder.
Meiri asks the same question as Tosafot, but gives other suggestions as to what the mishnah is prohibiting, including betzeikot shel akum - matzah manufactured by non-Jews, which cannot be used to fulfill the mitzvah of matzah at the seder, as it was produced shelo lishmah.
So it seems clear from Meiri that one is allowed to eat such matzot on erev pesach.
Maharsha infers from Tosafot, who only suggest the eating of matzah ashirah on erev pesach, that they would prohibit matzah shelo lishmah. The rationale is that matzah shelo lishmah tastes exactly the same as matzat mitzvah, and would therefore be prohibited (as opposed to matzah ashirah which tastes different from matzot mitzvah).
Rambam writes in Hilchot Chametz uMatzah 6:12:
אָסְרוּ חֲכָמִים לֶאֱכֹל מַצָּה בְּעֶרֶב הַפֶּסַח כְּדֵי שֶׁיִּהְיֶה הֶכֵּר לַאֲכִילָתָהּ בָּעֶרֶב.
The sages have forbidden the eating of matzah on the day preceding Pesaḥ, in order to make it conspicuous at night.
One could make a convincing case that Rambam would include eating matzah shelo lishmah in this prohibition, as it is not sufficiently distinguishable from the matzah one will eat at the seder.
That being said, Rabbeinu Manoach (ad loc.) does allow eating betzeikot shel akum on erev pesach.
R. Betzalel Zolty in Mishnat Ya'avetz Orach Chaim 16:5 argues for the approach of Meiri, and is willing to permit eating matzot produced shelo lishmah on erev pesach.
In contrast, R. Yitchak Ya'akov Weiss in Minchat Yitzchak VIII:37 strongly opposed using this innovation in practice.
R. Shlomo Zalman Auerbach is quoted in Shemirat Shabbat keHilchatah 56 f.n. 47 as also being opposed to the practice. He notes that any matzah which we would be willing to eat on erev pesach must have been specifically protected from turning into chametz. He believes that that in itself may be sufficient (lechumrah) to make it matzah lishmah, which would preclude its being eaten on erev pesach.
R. Neuwirth notes that maybe one could distinguish between matzot produced without a specific intention that they be used for matzat mitzvah, where R. Shlomo Zalman's issue would arise, and matzot manufactured with specific intention that they not be usable for the mitzvah, which possibly could be eaten on erev pesach, even if they were manufactured while being protected from becoming chametz.