The only areas that will present difficulty in a fully assembled car are dome light (headliner), power windows, power seat, power top, door jamb switches (kick panel).

The dome lamp harness is clipped to the roof rail with plastic clips, so you cannot just pull the old wire and fish the new one back. Well, you can, but you'll likely see the wire laying on top of the headliner.

To do the rear body harness, just remove the left kick panel, door sill trim plate, galvanized wire guards (pull back the edge of the carpet), rear seat, and rear quarter inner trim. The harness can be pulled out and fished back through without much difficulty.