First I advise you to read some ASM tutorial, the one made by FBI agent is pretty good.
Try to make sense with the things you read, and if you have any problem, you can pm me on come on the chat
I didn't look into it so I'm not sure how to nuliffie other items. But I do know how to create new effect. Look at my lightball/timespace orb routine, I created items that boosts some stats/attack for specific pokemons. See if you can do the same. If you have trouble doing so, I'll be glad to help you