Can we add solar lights to rented porta potties for an evening wedding?

Ask the rental company before you attach anything, and keep lights freestanding instead of screwing or sticking them to the plastic.

Most rental contracts treat the cabinet as their property. Drilling a bracket, zip-screwing into a wall, or peeling adhesive later is how people pick up damage charges on a standard unit or an ADA unit. For evening receptions I have run, the cleanest setup is stake-in solar path lights along the walk from the tent, plus a couple of freestanding battery lanterns near the doors. Guests can see where they are going without touching the cabinets.

Inside a stall, a small battery lantern hung from the coat hook (if the unit has one) works fine. Skip tape, Command-style strips, and anything that leaves residue on the walls or ceiling. Same idea on the ADA unit: light the approach and keep the doorway clear so a guest with a mobility aid is not navigating in the dark.

Confirm with the company that ground lights and hook-hung lanterns are okay, and that the service crew will leave them alone during a pump-out. That call beats guessing after delivery.