Pre-built means they are built on OEM cores. All orders are built to order and not upgradable with any options. The builds are standardized with pre selected options.To avoid downtime with your car, we have a pre-built option that'll allow us to customize a separate set of cores while you still have your current headlights. Every pre-built order is required to have a core deposit. When an order is placed, we will begin sourcing and customizing a separate set of cores, making them brand new tailored towards your desired customizations. Afterwards your new headlights will ship out to you. Once they arrive we recommend removing your old headlights and installing your new customized headlights immediately. After installing, you have 30 days from your delivery date to ship your old headlights to us, otherwise the additional deposit will be forfeited. Please use our boxes and packing material that were delivered to you. Write your order number inside or outside of the box where it's visible for us to find and ship your old headlights to us. Once they arrive we will inspect your headlights for damages. If your original cores were sent with damages, BayOptiks will either deduct a portion of your deposit or retain your deposit. Damaged lenses are acceptable. After passing our inspections, we will then refund your core deposit deposit. Please ship your old headlights to: 6743 Dublin blvd, #17, Dublin, CA