How do I assign account numbers to customers?

Hi

How do i give customers a acount nummber? and on the invoice it need to be under the Name or address
if you have 2 customers with the same name and surname to use for EFT Ref.

Like
Hennie Groenewald
Account No: Gro001
15 Wilson Straat,
Witfield

Or
Hennie Groenewald
15 Wilson Straat,
Witfield
Account No: Gro001

use the Code field beside the Customer Name when creating a customer.