He must not replace it or exchange it, either good for bad or bad for good. But if he does substitute one animal for another, both that animal and its substitute will be holy.

Leviticus 27:9
If he vows an animal that may be brought as an offering to the LORD, any such animal given to the LORD shall be holy.

Leviticus 27:11
But if the vow involves any of the unclean animals that may not be brought as an offering to the LORD, the animal must be presented before the priest.

Leviticus 27:33
He must not inspect whether it is good or bad, and he shall not make any substitution. But if he does make a substitution, both the animal and its substitute shall become holy; they cannot be redeemed.'"

Ezekiel 48:14
They must not sell or exchange any of it, and they must not transfer this best part of the land, for it is holy to the LORD.

He shall not alter it, nor change it, a good for a bad, or a bad for a good: and if he shall at all change beast for beast, then it and the exchange thereof shall be holy.