Customer ID

The customer ID field is auto-assigned and cannot be changed. You can however set a custom Customer Code. You can then search by Customer Code in any customer auto-complete boxes in addition to the customer's name.

You can display the Customer Code in search boxes by turning on the setting Admin -> Billing -> Company Options -> General -> General -> Show Customer Code In Auto Complete Boxes.

You can have the system automatically create an incrementing series of customer codes when new customers are added by turning on the option Admin -> Billing -> Company Options -> Defaults -> Customers -> Generate Customer Code For New Customers.