Leviticus 27:10 anticipates the worshipper having second thoughts. With such double mindedness, the worshipper may attempt to substitute an inferior animal in the place of the one which was dedicated. Leviticus 27:10 stipulates that the worshipper may not exchange what he has promised. No redemption is possible once the animal has been donated. If the worshipper attempts to deceive the priest by exchanging the animals, then both animals are forfeited and now belong to the Lord.
10 He shall not exchange it or make a substitute for it, good for bad, or bad for good; and if he does in fact substitute one animal for another, then both it and the substitute shall be holy.