Do I need to cut or splice into my factory wiring?

No. The harness connects to your existing loom at the factory junction points. The switch mounts where your Accent's dash design supports it — no rewiring the steering column.

Will these fit under my stock bumper, or do I need to modify it?

These mount at the factory fog light positions on 2003-2006 Accents. If your bumper doesn't have those openings already, you'll need to check fitment with your specific bumper design before committing to the install.

What bulbs do I need, and are they in the box?

Bulbs are not included. You'll need standard H3 or equivalent fog bulbs (check your vehicle manual for the exact spec). Grab them separately and drop them in when the lights arrive.