The code can be put in either bootloader or bootloadable.
Both the bootloader and the bootloadable can use this section.
Do you mean the rows of checksum exclude area? Usually it is the last row(s) in User Flash area. The exact row number....can put a specified sequence such as 0xAA, 0xAA 0xAA......in exclude section, and users can check the exact address in PSoC Programmer.