Do these bolt straight into the factory headlight buckets without modification?

Yes. These mount at factory points — no drilling, cutting, or bracket fabrication required. Pull the old headlights, drop these in, and reconnect the wiring harness.

Will I need to replace my wiring harness or add a relay?

Wiring configuration is not specified in the product data. Before installation, test the connector fit at your vehicle's headlight port. You may need an adapter or harness if the plugs don't match OEM.

Are the LEDs soldered in, or can I replace individual bulbs later?

The LED light source is integrated into the assembly — it's not user-serviceable. If the LEDs fail, the entire headlight will need replacement.