3rd Perek Summary: “Elu Kedoshim”: The laws of “exchange” of a sacrifice and of the embryo of a sacrifice are similar, except that an “exchange” does not make a further “exchange,” while an embryo can make another embryo (assuming it’s female).
The “exchanges” (and embryos) of voluntary sacrifices take on the identity of the original sacrifice: shelamim, olah, as well as firstborn and tithe.
The “exchange” of a todah is brought as a todah, but without the attendant breads.
Obligatory sacrifices that are “exchanged” (and the embryos) have a different law. An asham “exchange” is considered as if it had been invalidated is allowed to graze until it receives a blemish and then it is sold and with the proceeds a communal olah is sacrificed. The same procedure is done if someone mistakenly consecrated a female animal for an olah or asham (which only come from males). One brings an olah in place of the olah and a communal olah in place of the asham.