Repeating the marriage contract in the mosque after conducting it one's house
I conduct marriage contracts at the house of either the groom or the bridegroom in front of their families and a limited number of people. After the contract, the marriage is publicized in the mosque by repeating the marriage formula in front of an audience and guests. Some people object to this on the pretext that the Prophet did not practice it.
The marriage formula indicates a propositional statement rather than a performative or declarative one. However, it was necessary to shift the meaning to convey declaration for the purpose of effecting the marriage contract and so the meaning of the words would reflect the external reality of the performance of the marriage contract, and not a simple declaration to which the possibility of falsehood may be attached. Formulating contracts is an important and valid objective that requires replacing the propositional nature of the formula (the default) with the declarative/performative one.
If, after conducting the marriage contract, the marriage formula is repeated once more (in its default propositional sense) to indicate that the event has indeed occurred, this is both linguistically correct and permissible in Islamic law. Such an instance may include the bride's guardian telling her husband, "I have given my charge to you in marriage," and the husband answering, "I have accepted" whereby both intend to inform of a past event and not formulate a new contract. In light of this interpretation, the meaning of the bride's guardian's words would be, "I have given my charge to you in marriage since …" and the meaning of her husband's words would be, "I have accepted [your offer] from that time." There is no legal objection to this.
Claiming that the repetition of the marriage formula is impermissible on the pretext that the Prophet did not practice it is unsound. This is because the non-existence of evidence that the Prophet refrained from a certain act does not mean that he did not actually practice it. Even if we were to assume that the Prophet did not perform this act, this does not necessarily mean that it is impermissible. In the principles of Islamic law, it is invalid to maintain the impermissibility of the acts which the Prophet did not perform.
Based on the above, the practice mentioned in the question is valid and permissible in Islamic law.
Allah the Almighty knows best.