Is it permissible for a Hafiz of the Quran to lead prayers in a mosque where innovations (bid'ah) are prevalent, and there is no other mosque available, given the inability to prevent the muezzin from performing innovations after the prayer and before the iqamah?

There is no harm in you praying in the aforementioned mosque. However, it is better to pray in a mosque free from innovations (bid'ah) if that is possible. There is no objection to leading prayers in this mosque, provided you do not participate in the innovations, and you continue to advise those in charge and explain to them the concept of bid'ah.