Q: Our bishop is going to preside at wedding in choir dress, while a priest will be the celebrant. Does the bishop do anything special?
A: His vesture is described in the Ceremonial of Bishops, 601: alb, pectoral cross, stole, and white cope, using the miter and pastoral staff.
I read 611 to say that the priest as celebrant introduces the nuptial blessing, but the bishop as presider gives it.
Otherwise, it’s business as usual.