I know that you can customize the item editor menu with init.org, but the item editor menu shows only after you click to open an item.
Is there a way to customize the swipe and/or long press menu just like the item editor menu?
It isn't currently possible to customise this. What sort of things are you looking to add?
I've added this feature - I'm planning on using this myself. I hope to release an update with this later this week/next week.