Being proactive shows that you are a team member willing to share your experience to bring swift resolution. Most of the time the architect has the power to approve for the client. However, sometimes the client has retained that privilege alone. This can become a very important legal point later. So know up-front whose signature must appear.
Process change orders throughout the job.
I guarantee you that your client will not be a happy camper and you may be out the money. Get it in writing as you go. Project closeout must begin with the startup phase. The submittal log must indicate what is required for proper closeout from each trade. Do not wait until the end of the job to begin gathering this information.