When I change the Config option to true, the block/item doesn't show up. And what are thoe getSubBlocks()/getSubItems() methods you are speaking of? Why do I need them?
They are meant for blocks that differentiate between metadata (and show multiple blocks in the creative tabs), but, if you use it to return an empty list, it will show nothing in the creative tabs, not even in the "all items" tab. Which, I assume, you would want.
Hm. Basically I want to have a config option where the user can choose wether he wants the e.g. Slime Portal in the More Dimensions Creative Tab or not.