From: Rabbi Moshe Sofer
To: Rabbi Mordechai Leib
The Chasam Sofer rules that although an assailant of a Torah scholar is technically under automatic cherem, in a community where enforcement is impossible and the offender would only mock resistance, the pious individuals should not withhold their Amen responses, as doing so would harm only themselves spiritually with no effect on the offender. Regarding the Kohen who took an aliyah after the rabbi was displaced by a higher bidder, the Chasam Sofer rules the Kohen bears no blame, as the disgrace was caused solely by the bidder, and the rabbi's waiver of his own honor cannot override the Kohen's priestly precedence.
Source: Shu"t Chasam Sofer CM §182