Is it permissible to convert a small, abandoned mosque, due to the presence of another mosque nearby, into other uses such as housing?

It is permissible to replace a waqf (endowment) if there is a recognized benefit or to avert a harm, as is established in Sharia by bringing about benefits and repelling harms. Many scholars have supported this, such as Sheikh Ibn Taymiyyah, Sheikh Ibn Uthaymeen, and Dr. Khalid Al-Muslih, citing the action of Umar ibn al-Khattab, may Allah be pleased with him. Accordingly, there is no objection to modifying a disused mosque to become accommodation for the Imam and Mu'adhin, provided that this is with the permission of the endower or supervisor, and that it remains an endowment.