Hi there,
If you look down the RH crawl way on the top of the MAWEA you will see the aircraft registration and airline two letter code. This is the AC ID coding panel. This supplies aircraft identity to systems like the FMS, CMC, ACMS and so on.
The Transponders are Pin Programmed with the ICAO 24 bit address for the aircraft. Have a look at the ASM/WDM and you shall find the info.
There's no info in the AMM as Boeing charges for a modification package to change the aircraft identity. I know as wrote a series of Part 21 modifications to do the same.
For info SELCAL is the same too as it's pin programmed as well.
Jimpy