Make sure he(she) knows what you plan to do. It would be best to have some of this veneer on hand.

Electrician can either mount the receptacle boxes further out to allow room for the veneer, or they can get a deeper box for a few cents more.

The problem that occurs is that standard boxes are not set up for arbitrary thickness walls.

They have some room, but if nailing flanges are going to be used they need to fall on the studs or blocking.

The front edge of the box must be recessed no more than 1/8 inch behind the face of a non-flammable surface.

Box extensions are another way of making up for wall thickness.

Thin ones go under the mounting yoke of devices and are held by the device mounting screws.
Deeper extensions use there own screws to attach to the box ad provide mounting tabs with holes for the device to than attach.

You may have to trim the device mounting screw length, but that is a simple thing.

Adjustable boxes are offered by more than one manufacturer. I do think you are wise to communicate with the electrician about the plans. Too often, it is wrongly assumed that he/she knows all about future plans for wall thickness and finishes.

Here is a link that might be useful: Carlon