Tip: You can use Lunar Magic's Overworld Layer 3 Editing system to edit or create your own layer 3 images (castle bricks, fish, rocks) and apply unique effects per level via the Layer 3 Bypass in the main editor.
This patch allows you to have cursor in the message box to select between multiple options.
The message box opens and closes like usual and can be edited in Lunar Magic.
Note: The selection only stores a value to a RAM address, if you actually want the selection to do something, you'll have to code that yourself (meaning, ASM knowledge is required)
The part where you want to edit the code is a bit below, shouldn't be hard to find.
For further information, see the readme.