Halakhah zu Wajikra 27:26

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 first-born a burnt-offering nor a peace-offering nor any other sacrifice. And the received tradition comes that it is not specifically with a first-born 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 first born. 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.