Is expiation permissible before the fulfillment of a condition attached to a potential Zihar?

Primary text

If a man tells his wife, 'If you enter the house, you are to me as the back of my mother,' expiation is not permitted before she enters the house. This prohibition exists because it constitutes presenting the expiation before the Zihar act itself (which is conditional upon her entry). If he manumits a slave for Zihar expiation, and then she enters the house, the slave becomes free, the man becomes subject to the ruling of Zihar, but the manumission does not suffice as expiation because the Zihar was conditional, and its ruling cannot manifest before its condition is met.