Does the agreement of the spouses to replace some of the marital home’s furnishings (part of the dowry) with other more suitable pieces affect the validity of the marriage contract or entail anything?

There is no objection to the husband disposing of the household furniture owned by his wife, with her permission. This does not affect the validity of the marriage contract, whether he replaces some of the furniture with similar items or different ones. It is permissible for the wife to gift her dowry to her husband, and it is permissible for him to accept it, as Allah Almighty says: "And give women their dowries as a free gift. But if they are pleased to give up to you therefrom anything, then consume it with good cheer and satisfaction."