Rom Expansion Explained - haven1433/HexManiacAdvance GitHub Wiki
This utility makes your rom bigger or smaller. GBA roms are usually between 16 MB and 32 MB (
0x2000000 bytes). You can specify any hexadecimal (base 16) number between 0x1000000 and 0x2000000 to assign a new file size in bytes. Alternatively, you can type any decimal (base 10) number between 16 and 32 to specify the number of megabytes the ROM will have.
Warning: If you specify a number of bytes/megabytes that's less than the current ROM's file size, then the file will be truncated, and you will lose whatever data got truncated. Having a backup of your ROM before truncating your ROM would be wise.
... What else do you want?