How can one deal with the pervasive authority of social custom, which compels an individual to perform certain actions, such as offering condolences or congratulations, not with the intention of performing the act itself, but rather in response to this authority?

A Muslim must submit to the judgment of Allah Almighty and apply His law to the customs of people. Whatever customs are legislated, the Muslim acts upon them in compliance with the divine command, and it is permissible to follow permissible customs. However, whatever the Sharia (definition) has forbidden, it is not permissible to follow customs in that regard. Offering condolences and expressing sympathy are religiously encouraged, on the basis of a recommendation. As for innovations related to mourning, one must avoid them and not follow people in them.