Is it permissible for a committee overseeing a mosque to dispose of funds allocated for a specific purpose (such as restrooms) and spend them on another purpose, when the majority holds this view?

The first and most prudent approach is to spend the money on what its donor designated it for, if it is a permissible or lawful cause. However, if there is a need or necessity to spend it on the mosque's construction, then there is no harm, because building the mosque is better and of greater benefit, and it is the primary objective. As for building restrooms, it falls under the category of means to facilitate the performance of prayer.