Will this work with an aftermarket rear bumper?

This bar is designed around factory bumper geometry. If you're running an aftermarket bumper, test-fit it first — mounting point locations may differ, and you might need to modify the bar or use alternative fasteners.

Does this affect trailer hitch clearance?

The reinforcement bar mounts behind the bumper cover and doesn't extend beyond the factory rear overhang. A factory or aftermarket hitch will clear it, but verify fitment if you've modified the rear overhang or installed non-standard hardware.

Can I paint this before or after installation?

Paint before install — it's easier to handle off the car and lets the paint cure without risk of overtightening fasteners over a fresh coat. Use self-etching primer designed for hard panel materials, then topcoat to match your bumper.