I suspect, that exposing and lighting for the "Christmas Lights" to show up great, will have a serious negative effect on the quality of the faces of the wedding party, including the bride and groom, and guests.
By lighting the faces so they show up well, the amount of light there, and the exposure to allow it to show the faces well, will negate the lessor brightness of the "Lights."
The question is, which is more important, great images of the lights, or great images of the people? Read that bride and groom. They might want the "Lights" today, but I suspect, when the photos come in, it will be everyone's faces which will be paramount in their desires, and then it will be too late, and disappointment and upset feelings will rein supreme.
You must absolutely test to be sure this is so. If I'm right, you should go back to the couple and discuss this.