The rgbfix program changes headers of Game Boy ROM images. It also performs other filetype operations, such as truncation. The arguments are as follows:

-C
    Set the Game Boy Coloronly flag: 0x143 = 0xC0. If both this and the -c flag are set, this takes precedence.
-c
    Set the Game Boy Colorcompatible flag: 0x143 = 0x80. If both this and the -C flag are set, -C takes precedence.
-i game_id
    Set the game ID string (0x13F0x142) to a given string of exactly 4 characters. If both this and the title are set, the game ID will overwrite the overlapping portion of the title.
-j
    Set the non-Japanese region flag: 0x14A = 1.
-k licensee_str
    Set the new licensee string (0x1440x145) to a given string, truncated to at most two characters.
-l licensee_id
    Set the old licensee code, 0x14B, to a given value from 0 to 0xFF. This value is deprecated and should be set to 0x33 in all new software.
-m mbc_type
    Set the MBC type, 0x147, to a given value from 0 to 0xFF.
-n rom_version
    Set the ROM version, 0x14C, to a given value from 0 to 0xFF.
-p pad_value
    Pad the image to a valid size with a given pad value from 0 to 0xFF. rgbfix will automatically pick a size from 32KiB, 64KiB, 128KiB, ..., 8192KiB and give a warning thereafter. The cartridge size byte (0x148) will be changed to reflect this new size.
-r ram_size
    Set the RAM size, 0x149, to a given value from 0 to 0xFF.
-s
    Set the SGB flag: 0x146 = 3.
-t title
    Set the title string (0x1340x143) to a given string, truncated to at most 16 characters. It is recommended to use 15 characters instead, to avoid clashing with the CGB flag (-c or -C). If both this and the game ID are set, the game ID will overwrite the overlapping portion of the title.
-v
    Validate the header and fix checksums: the Nintendo character area (0x1040x133), the header checksum (0x14D), and the global checksum (0x14E0x14F). 