Maaser Sheni, Chapter Three, Mishnah Four
This mishnah teaches ways in which a person who has maaser sheni money in one place and hullin (non-sacred) produce in another can exchange one for the other.
1) If [one had hullin] produce in Jerusalem and [second tithe money] in the provinces, he may say: Let that money be exchanged for this produce.
2) If [he had second tithe] money in Jerusalem and [hullin] produce in the provinces, he may say: Let this money be exchanged for that produce, as long as he will carry that produce and eat it in Jerusalem.
Section one: Even though the produce and the money are not in the same place, a person can buy the produce with this maaser sheni money. He can now eat the produce in Jerusalem and when he gets home he can use the money for whatever he wants.
Section two: In this case the second tithe money is in Jerusalem, but he wants to use the coins to buy something besides food. What he can do is state that the moneys sanctity will be transferred to the hullin produce that he has outside of Jerusalem. He can then use the money for whatever purpose he wants. However, later he must bring that produce to Jerusalem. He cannot again redeem the produce and then bring the money to Jerusalem.