I highly recommend having strong documentation, visual demonstrations, and the presence of relevant developers and team personnel. Your job is to lead the client to the best solution for them. Use all the ammunition you've got. The more you can represent visually, the easier your job is. Use diagrams for process changes.
Prototype changes to the user interface.
Demonstrate the gap in the developing product that is leading to the change request. Have a whiteboard handy to draw things on. Back to the Client. Once you've considered these five questions, you are ready to bring the change request to the client. You can gather all or a quorum of client decision-makers in one room, and present the issue and the solution options.