ESV Numbers 30:
10And if she vowed in her husband’s house or bound herself by a pledge with an oath, 11and her husband heard of it and said nothing to her and did not oppose her, then all her vows shall stand, and every pledge by which she bound herself shall stand.
12But if her husband makes them null and void on the day that he hears them, then whatever proceeds out of her lips concerning her vows or concerning her pledge of herself shall not stand. Her husband has made them void, and the LORD will forgive her. 13Any vow and any binding oath to afflict herself, her husband may establish,b or her husband may make void.
14But if her husband says nothing to her from day to day, then he establishes all her vows or all her pledges that are upon her. He has established them, because he said nothing to her on the day that he heard of them. 15But if he makes them null and void after he has heard of them, then he shall bear her iniquity.”
The husband was not allowed to just wait and see what would come of her vow. Being head of the wife (Ephesians 5:23), he had to bear the consequences of his wife's sin as if he had made the vow.
4 or if anyone utters with his lips a rash oath to do evil or to do good, any sort of rash oath that people swear, and it is hidden from him, when he comes to know it, and he realizes his guilt in any of these; 5when he realizes his guilt in any of these and confesses the sin he has committed, 6he shall bring to the LORD as his compensationa for the sin that he has committed, a female from the flock, a lamb or a goat, for a sin offering. And the priest shall make atonement for him for his sin.
then he shall bear his iniquity: be accountable for the breach of the vow, the sin shall be reckoned to him, and he shall bear the punishment of it, because he ought to have declared is disapprobation of it sooner;
Geneva Study Bible expresses a similar sentiment:
Not the same day he heard them, but some day after, the sin will be imputed to him and not to her.
Does the Husband become "sinful" when revoking His wife's prohibitions?
Yes, being the head of the wife.