3,518. Transferring the Sanctity of Second Tithe Money to Produce or Animals
Hilchos Maaser Sheini and Neta Revai 4:6
The sanctity of second tithe money may not be transferred to produce (outside of Jerusalem); if one did so, the produce to which he transferred the sanctity must be brought to Jerusalem and eaten there. The sanctity of second tithe money likewise may not be transferred to live animals or birds. If one made such a transfer, it is ineffective and the sanctity is not transferred. The Sages instituted this restriction out of concern that one might raise such animals in herds. (If one did so, the offspring of those animals would also be sanctified.) If one transferred the sanctity of second tithe money to animals that had been slaughtered, they are considered food and must be brought to and eaten in Jerusalem. The money then reverts to its previous secular status.
Hilchos Maaser Sheini and Neta Revai 4:7
In a case of great need (specifically a case that will be discussed IY”H in halacha 6:2), one may transfer the sanctity of silver coins to brass coins. However, one may not leave the brass coins in their sanctified state. Rather, he should transfer the sanctity from the brass coins back to silver as soon as he is able.