There should be some type of poison or something where you can make your already bought weapons poisonous instead of having to re buy the same item with a poison feature. Or make an item upgradeable where you can make it poisonous with a certain amount of upgrades

you dont re-buy poison gas bomb, but you can only use it once each battle. Unless I guess if you buy more of them.

I meant for jutsus since some jutus require you to have certain items one in perticular i want requires the user to have some type of poison

I guess... maybe post your question on an actual jutsu that would require it...