It is not just for the custom of performing Melachah on Erev Pesach (that is related to a Torah prohibition, where we say that one is required to accept the stringencies of both places) - it even applies to a custom that they accepted (which certainly has no source in the Torah) - for example, the following accepted to refrain from their melachos during Chol HaMoed -

Hunters laying nets in Teveryah.

Chopping beans in Tzipori.

Grinding wheat seeds (for porridge) in Acco.

Question: 2. and 3. are understandable, as they are both edible without chopping/grinding or by preparing a large amount before the festival. But refraining from laying nets will surely cause a reduction in the celebration of the festival?!

Answer: They could hunt using hooks or other traps that would not be so apparent to the public, thereby not reducing the celebration of the festival.

R. Imi cursed those hunters who refrained from laying nets as they were reducing the celebration of the festival.

Question: If they travelled from their town to another place where the custom was to permit it, must they continue with the prohibition or may they take on the local custom to permit it?

Answer: It should follow the case of R. Ba that the people of Mysha accepted upon themselves to refrain from sailing across the (Mediterranean) sea (since in the place that they originally lived, that was the custom, out of concern that it would cause Shabbos to be broken). They came to Rebbe and told him, "Our forefathers had the custom not to sail across the sea. What should we do?'' Rebbe replied, "Since your forefathers had the custom to prohibit it, do not change from the custom of your forefathers.''

Question: Surely it should be like a Neder (vow) that a person should not be able to retract?

Answer: There, the one who vowed is asking to retract. Here, it was the forefathers who vowed.

Question: All the more so that it should be permitted?!

Answer (R. Chananya): It was not for the reason of the forefathers' vow that Rebbe prohibited it. Rather the reason was because Rebbe was a student of R. Yuda who held that it is actually prohibited to sail across the Mediterranean.

Question (R''L to R. Yochanan): Is it not prohibited because of the Pasuk, "Bal Sisgodadu'' - "you should not split into groups''?

Answer: This applies when these follow Beis Shammai and these follow Bei Hillel, but when they are accustomed to act stringently upon themselves, it is not prohibited.

Question (Reish Lakish): But in a dispute between Beis Shammai and Beis Hillel, the Halachah follows Beis Hillel (and those that follow Beis Shammai are anyway not correct - see Pnei Moshe)?!

Answer (R. Yochanan): Rather it applies, for example, when these are following R. Meir and these are following R. Yosi.

Question (R''L): But in a dispute between R. Meir and R. Yosi the Halachah follows R. Yosi (so a Pasuk is not required to say that one may not follow R. Meir)?

Answer (R''Y): The are two versions as to the opinion of R. Meir and two versions as to the opinion of R. Yosi, with some ruling like R. Meir and some like R. Yosi - in this case there is a prohibition of "Bal Sisgodadu''.

Question (R''L): Concerning sounding the shofar on Rosh HaShana and Yom Kippur of Yovel, in Yehudah their custom is like R. Akiva (that they blow for Malchiyus) and in Galil their custom is like R. Yochanan ben Nuri (that they do not blow for Malchiyus - why is it not a transgression of "Bal Sisgodadu'')?

Answer (R''Y): Since all agree that if one transgressed and acted in Yehudah like the custom of Galil or vice-versa, he has fulfilled his obligation - therefore it does not look like there are two Torahs.

Question (R''L): On Purim, some read on the 14th of Adar and some on the 15th?

Answer (R''Y): The one who arranged the Mishnah based it on the Pasuk that refers to each family, each country and each city. This is instructing a variation in the times that the Megillah is read; therefore it is not a transgression of "Bal Sisgodadu''.

Question: It is fine if he goes from a place where Melachah is done (on Erev Pesach before noon) to a place where it is not done (if he follows the local custom, he is not transgressing and he is not causing dispute). But if he goes from place where it is not done to a place where it is done, what should he do? (If he does not work, he is causing dispute; if he works, he is transgressing as he comes from a place where they do not work

Answer: He should not work, as there are others there who do not have work to do.

(R. Simon quoting R. Yochanan): The Mishnah is referring to a person who consistently has work. If he would refrain, it would be very surprising. Therefore, he would cause dispute by refraining and must work if the custom in his new location is to work. (Note: This follows Korban Ha'Edah's second explanation)

(Mishnah): Similarly, one who brings Shevi'is fruit from a place where there is no more such fruit in the fields for the animals (therefore the dwellers there must destroy all such fruit from their homes), to a place where there still is such fruit, or vice-versa, he is obliged to destroy them.

R. Yehudah says "Go out yourself and also bring'' (the Gemara will explain this).

(Gemara - Explaining R. Yehuda): If they had ended in Teveryah but not in Tzipporin, he may say in Teveryah, "Go and bring from Tzippori''. This is not a cause of dispute as such fruit can be brought from a permitted place.

(R. Chananya & R. Pinchas): R. Yehudah and R. Yosi are of the same opinion, as the Mishnah teaches (in Maseches Shevi'is) -

Shevi'is fruit may be eaten if ownerless fruit exists of the same type.

It may not be eaten if there only remains such fruit on vines in a guarded place (as it causes suspicion).

R. Yosi says that such fruit may be eaten, as he can say to them, "You can go there and take it yourselves''.