From: Rabbi Moshe Sofer
To: Rabbi David
When an elderly yavam and yevamah mutually agree to remain in zikah and neither party has any claim against the other, the Chasam Sofer rules that beis din has no authority to compel either yibum or chalitzah. He further rules that the Zohar's teaching that chalitzah benefits the deceased's soul creates no enforceable obligation, but describes a voluntary spiritual remedy akin to reciting Kaddish — one cannot be compelled to follow the Zohar against the explicit ruling of the poskim.
Source: Shu"t Chasam Sofer EH II §85