it is impossible to do that unless you start the game over again and don't collect the item you don't want
You can unregister them but you can't remove them from your pack
Key items are impossible to trade or remove, except to Pokémon Colosseum.
Unduplicatable ItemsThe only Items you can't duplicate in Emerald are Mails, because you can't store a Pokemon holding Mail into a PC. You can't clone any Key Items either.
To get to new mauville
Code name: All Key ItemsCheat device: GameSharkGame version: EmeraldCode:B97754ECD579A62C013265005FC4BF056CCE16E8BE01460A5FC4BF056CCE16D97F91DCA676A3A1737D585FC4BF056CCEF95F96DCC3F970A3A171FD485FC4BF056CCEF0268068361D39DE786746915FC4BF056CCE80300821AC1839C47C65EC805FC4BF056CCEF046806BBC9C5FC4BF056CCE66BEB4699203F03B95F0DC4E5FC4BF056CCEE63E94699205F03B95F0DC4E5FC4BF056CCE1FD8BF055CCEF03B95F0DC4E5FC4BF056CCE9F589F055CC8F03B95F0DC4ENote: Code not personally tested.
As far as I know there is no code for key items.
Ruby & Sapphire Key
You can unregister them but you can't remove them from your pack
Key items are impossible to trade or remove, except to Pokémon Colosseum.
Unduplicatable ItemsThe only Items you can't duplicate in Emerald are Mails, because you can't store a Pokemon holding Mail into a PC. You can't clone any Key Items either.
you can't
When facing water, open your bag and go to key items. There select the Super Rod and then use it.
There is no key it opens when you become a Pokemon champion.
select
you can't delet key items in any Pokemon games.
Watson gives it to you
where you use the key to turn on the quary.