What is the ruling on stepping forward to lead the prayer when the Imam's deputy is present?

If a mosque was built by its congregants, then the Imam does not have the right to appoint someone else without the consultation and consent of the mosque's congregants. They have the right to put forward someone they approve of. As for mosques built or endowed by the state, where a salaried Imam has been appointed, he is permitted to delegate [someone else to lead prayer] due to an excuse, and his deputy has more right to lead the prayer than others. Giving precedence to someone other than the deputy is disliked (makrooh).