At this moment it is not possible to change your line-ups in any way. When we made the rules, we didn't plan any mercato as well.
But as our goal is to make TRC a very democratic competition, we can re-open this discussion. First, us admins will see if there is such possibility, and second we will ask for all other teams opinion.
So please, if you already made a change in your first post, undo it. We will consider only the previous LU, the one we have the Qualifications database.
I'll come back to you shortly as soon as TRC Admins take a decision.