There should be a sprite-ish thing called Global Custom Blocks. It's not a sprite, it goes in the sidebar with the stage. You don't see it so it doesn't need a preview. The global custom blocks you want to make go there. In that “sprite” you can't click blocks to run them. In it you also can drag out all blocks except hats. So it would have both next costume and next backdrop, but not when green flag clicked. Custom blocks you define here will be available throughout the whole project.

I don't get what youre saying. this is confusing