ROM patch codes are a special type of code which intercepts reads to
the cartridge's data. There are several limitations in using these
codes.
Action Replays have four 'ROM Patch Slots' - numbered 1 through to 4.
Only 1 code can be used in each slot at a time. All ROM Patch codes
in this guide are labelled with what slot they occupy.
YOU CANNOT USE TWO CODES THAT SHARE THE SAME ROM PATCH SLOT.
Many codes in this guide have been encrypted for more than one ROM
Patch Slot - you only need to use one of these codes.
For example, the Wild Pok?mon Species Modifiers use two ROM Patch
slots - slots 1 and 2. If you want to use the Level Modifiers at
the same time, you cannot use the Slot 1 code, you -must- use the
Slot 3 code.
For VisualBoyAdvance users, there are no restrictions to the amount
of ROM Patch codes that you can have active at one time.
==Action Replay DUO Users==
According to the information I have, Action Replay DUOs are only
capable of having one ROM Patch code (note - 1 code is 2 lines)
active at any time. Therefore, the Shiny modifier and any other ROM
patch codes that take up more than one slot cannot be used.