Gemara

57a (Mishnah): If one said 'these Peros are forbidden to me', he may not benefit from Chilufeihem (what they are exchanged for) or Giduleihem (what grows from them).

47a (Rami bar Chama) Question: If one said 'this produce is forbidden to Ploni', may Ploni benefit from Chilufeihem?

One can forbid to himself something that is not yet in the world, for he can forbid to himself another's property. But since one cannot forbid Ploni's property to Ploni, he cannot forbid to Ploni Davar she'Lo Ba l'Olam!

Or, perhaps Chilufeihem are forbidden, just like Giduleihem!

Answer #1 (Rav Acha bar Minyomi - Beraisa): If a man told his wife 'you may not benefit from me', she may borrow, and the creditors collect from the husband.

Suggestion: It is as if the money she borrowed was exchanged for what her husband repaid, and she is allowed to benefit. This settles the question!

Rejection (Rava): Perhaps it is forbidden only l'Chatchilah to exchange what is forbidden, but b'Di'eved, it is permitted!

Answer #2 (Mishnah): If one was Mekadesh a woman by giving her Orlah (Peros within the first three years of a tree, which are forbidden), she is not Mekudeshes. If he sold the Orlah and was Mekadesh her with the money, she is Mekudeshes.

Rejection: Here also, perhaps it is forbidden l'Chatchilah to exchange Isur, but b'Di'eved it is permitted!

Chulin 4a (Beraisa): If Reuven keeps Chametz during Pesach, immediately after Pesach others may benefit from his Chametz, because he trades (his Chametz with that of Nochrim, to minimize his Aveirah).

Rishonim

The Rif (19b) brings Rami bar Chama's question about Chilufeihem of Konamos forbidding to someone else.

Rambam (Hilchos Nedarim 5:16): If Reuven forbade his produce to Shimon via a Neder or Shevu'ah, it is a Safek whether or not Chilufeihem and Giduleihem are forbidden. Therefore, Shimon is forbidden. If he benefited, he benefited.

Rosh (7:5): Rami asked about all Isurei Hana'ah, for we tried to answer his question from a Mishnah about Orlah. We know that one may not sell other Isurei Hana'ah. According to the opinion that "Lo Sochlu" forbids Hana'ah, the Torah permitted selling a Neveilah to teach that one may benefit from it (Pesachim 21b). B'Di'eved, the Torah permits Chilufei Isurei Hana'ah, except for idolatry and Shemitah (Kidushin 58a). Rami asks whether we fine the one who exchanged them and forbid Chilufeihem mid'Rabanan, just like Giduleihem. He does not distinguish Nedarim from other Isurei Hana'ah. Surely, they are permitted to others. If one kept Chametz over Pesach, after Pesach his Chametz is permitted, for we assume that he traded it with that of Nochrim (Chulin 4a).

Ran (47a DH Bo'i): Rami asked whether the Isur of Chilufeihem is because he intended to forbid them, or if Chilufeihem of all Isurei Hana'ah are forbidden to the one who exchanged them. If it is due to intent, a Noder can forbid to himself Davar she'Lo Ba l'Olam, but not to a Mudar.

Question (Ran): Why did he ask only about a Noder? If it is a general rule of Isurei Hana'ah, this applies even to a Mudar! Also, he should have asked about the Mishnah itself!

Answer (Ran ibid., and 57a DH Masnisin): The Mishnah (57a) always forbids Chilufeihem to the Noder, i.e. even if someone else exchanged it. This is because he said 'this produce', and made it like Hekdesh. Rami asked about when he himself exchanged it. Perhaps here also, it is forbidden only to a Noder. Or, perhaps in this case it is forbidden even to a Mudar.

Rosh (ibid.): The question was not settled.

Poskim

Shulchan Aruch (YD 216:1): If one said 'these Peros are Konam to me', he is forbidden Chilufeihem. Chilufei Chilufeihem are permitted.

Question (Taz 2): This is like the Ran. Why did the Shulchan Aruch ignore the Rosh (7:5), who explicitly forbids?

Answer (Nekudas ha'Kesef, Gra 3 and Korban Nesan'el 7:70): Surely, this is a scribal error in the Rosh. Kitzur Piskei ha'Rosh omits it. The Rosh merely cites the Mishnah, which permits. In Kidushin (2:31), he explicitly permits.

Shulchan Aruch (ibid.): The same applies if he did not say 'these', e.g. they were in front of him and he said 'they are Konam to me.'

Beis Yosef (DH u'Mah she'Chosav Rabeinu): This is like the Rosh (57a DH Masnisin). Perhaps the Ran would agree that even this is like specifying.

Rebuttal (Gra 4): This is wrong. (The Rosh says that any Konam that did not specify eating forbids Chilufeihem and Giduleihem. The Mishnah says 'these', for if he forbade the entire species, obviously Giduleihem are forbidden!)

Rema: Similarly, if he said 'Ploni's Peros' or 'Peros of the place Ploni are Konam to me', it is as if he said 'these Peros'.

Shach (4): The Levush says that the same applies if he forbade a species. This is wrong. The Ran (57a DH Masnisin) permits Chilufeihem in this case.

Shulchan Aruch (2): If he said 'what I eat or taste from them is Konam', if the seed disintegrates, e.g. wheat, Chilufeihem and Giduleihem are permitted. If it is Chasayos, even Gidulei Giduleihem are forbidden

Prishah (3), Drishah (4), Taz (4) and Gra (8): Regarding Chilufeihem, it makes no difference whether or not the seed disintegrates. The Shulchan Aruch, Rosh, Ran and Tur (if one looks into his words) permit in either case.

Rebuttal (Shach 6): There is no connotation to permit Chilufei Chasayos. Since Giduleihem are forbidden, Chachamim forbade also Chilufeihem.

Shulchan Aruch (ibid.): Similarly, if he said 'these Peros are forbidden to Ploni', Chilufeihem and Giduleihem are forbidden.

Shach (7): This is just like when he forbids to himself.

Beis Yosef (DH v'Chen): The Gemara did not settle Rami's question. The Ramban and Rosh did not rule about this. The Ran (47b DH ul'Inyan) is lenient, because it is a Safek mid'Rabanan. The Rambam says that it is a Safek, therefore he is forbidden.

Rebuttal (Korban Nesan'el Nedarim 7:90): It is clear from the Rosh in Kidushin (2:31) that he is stringent.

Question (Gilyon Maharsha): When he forbids to himself, it is Yesh Lo Matirim. When he forbids to Ploni, it is Ein Lo Matirim!

Answer (Shalmei Nedarim 47a DH b'Ran DH ha'Mekadesh): Since the Rambam forbids Reuven to give the food to Shimon, it is a Mitzvah for Reuven to permit his vow, therefore it is considered Yesh Lo Matirim.