there is different ways to make codes which are

1-*This is the easy way* searching values in nitepr (any cheat device u have for psp ex. nitepr rev k, mkultar 10.1, codepr )
or
2-*This is the hard way but is more for advanced codes*Learn MIPS and Use PS2Dis (dump the ram of the patch 1.6( analyze it and look for the code u want to make *