Halakha Imamat 27:26: Mishneh Torah, Negative Mitzvot & Sefer HaChinukh

Not to put frankincense on it, as it is said, “Nor put frankincense thereon” (ibid. 5:15).

Not to transfer a beast set apart for sacrifice from one class of sacrifices to another, as it is said concerning the first-born of cattle, “(The firstling of the beasts….) no man shall sanctify it” (Lev. 27:26); that is, no one shall offer it up as another kind of sacrifice.

To not change the consecrated from a sacrifice to a sacrifice: To not change the consecrated from a sacrifice to a sacrifice, such that we turn a peace-offering back into a guilt-offering, or a guilt-offering we turn back into a sin-offering — there is a negative commandment in this and that which is similar to it. And about this thing is it stated (Leviticus 27:26), “a man may not consecrate it” — meaning that he not make the firstborn a burnt-offering nor a peace-offering nor any other sacrifice. And the received tradition comes that it is not specifically with a firstborn that the verse is concerned — that the law is the same for all that is consecrated [for] the altar. As so did they say in Sifra, Bechukotai, Section 8:3, “I only have the firstborn. From where [do we know] about all the consecrated that we do not change it from [one] holiness to [another] holiness? [Hence] we learn to say, ‘with a beast, a man may not consecrate it.’” It hints that with every consecrated animal — whether the consecration of the consecrated for the altar or even for the upkeep of the [Temple] — we do not change it from its holiness, but it is [to be] left like it is; and “a man may not consecrate it” is stated about everything.