First, I would mention it to the EC to see if it is on his plans and tell him we're going to need it. I also mention the need to the GC since it is his job site. However, on a job site I have no authority to give another trade, or the GC a change order in any fashion, so my only obligation is to inform the customer.

It's just a simple professional courtesy to mention the add-on to the GC/EC. They should be paid for these changes and the only way that will happen is if the owner submits a RFC to the proper people.

I feel your pain, Jack. We're always the red-headed step child on job sites since we work for the customer, not the contractor.