hi

depending of the PIC you use, you can work work with a bootloader. see http://www.mecanique.co.uk/products/...ootloader.html

programming one time the bootloader with a programmer, allows you then to load your programm over serial connection.
the customer so can load over serial connection the hex file he get from you. he see only the hex file

i'm not sure if there is a way to change back the hex file into an asm file....