What is the ruling on some brothers' use of force to change mosque imams, what is the ruling on praying behind the new imam who was installed in this manner, and are there any implications for this?

The appointment of imams in mosques falls under the purview of the authorities designated by the ruler, and it is not permissible to dismiss an appointed imam and replace him with another without referring back to them. It is forbidden for anyone to lead prayer in a mosque that has a regular imam except with his permission or in his absence due to an excuse, because the regular imam has the most right to lead prayer in his mosque. Prayer behind an imam who shaves his beard is valid, but his case should be brought to the attention of the responsible authorities to replace him with a righteous imam if he does not perfect his recitation or if he has flaws. Wisdom and gentleness should be employed in dealing with people and in Da'wah (inviting to Islam), and severity and violence should be avoided.