In order to have the same LOADER for factory purposes (ISP) and IAP, I will use the same schema from ISP. I mean the same HEX format conventios plus some proprietary instrutions sets.
That is fine, but your bootloader must decipher the codes, the IAP functions do no such thing.
I mean, do I need to finish each record transmission with CR + LF. This is not so clear from the AN461
If you make your own loader, you must erase segments first (2nd and 3rd on page 13), the store the new program byte by byte using the PROGRAM BYTE IAP call (the first one on page 13 of rev 11).

When doing IAP it is your job to 'unpack' the .hex file.

Erik