John Wesley on Leviticus 27:10

He shall not alter it, nor change it - Two words expressing the same thing more emphatically, that is, he shall in no wise change it, neither for one of the same, nor of another kind: partly because God would preserve the reverence of consecrated things, and therefore would not have them alienated, and partly to prevent abuses of them who on this pretence might exchange it for the worse. It and the exchange - That is, both the thing first vowed, and the thing offered or given in exchange. This was inflicted upon him as a just penalty for his levity in such weighty matters.