I can’t tell you how many times people about to make a presentation decide, at the last moment, to change something crucial. Often they change the opening. It happens because a previous speaker gave them a new idea, or just because they had second thoughts.
When you change at the last minute you don’t have a chance to rehearse. No rehearsal means less confidence. And, when you don’t have confidence, the audience can smell it.
Give the presentation you planned and rehearsed. You’ll do great.