Is it permissible to abandon a recommended supererogatory prayer (Salat al-Tatawwu' al-Mandubah) if people believe it to be a Sunnah, as in the case of the supererogatory prayer before the Friday sermon?

It is permissible for someone who imitates those who hold the view that there is a Sunnah prayer before Jumu'ah to do so, and there is no accountability upon him. However, the more correct view is otherwise. So, he should perform what he considers a Sunnah, such as coming early for Jumu'ah and praying whatever Allah has decreed for him before the Imam ascends the pulpit. And if he speaks to them and explains the Sunnah to them in a kind manner, that would be good.