Q: If a eucharistic procession follows Mass, is it appropriate for a concelebrant to remove his chausable after Mass and wear something else? I thought priests wore their vestments in procession.
A: Here’s the quote from Holy Communion and Worship of the Eucharist Outside Mass (105):
“The priest who carries the blessed sacrament may wear the vestments used for the celebration of Mass if the procession takes place immediately afterward, or he may vest in a white cope.”
That tells me that concelebrants could remove the chasuble. And if there’s a delay before the procession begins, they could remove their vestments and join the procession in their street clothes.