You already have the solution in your question. You want to pass a reference of the list-box to a sub-vi to change the properties - so just pass it to the sub-vi.
Thomas
Using LV8.0 -------------------------------------------------------------------- Don't be afraid to rate a good answer... 😉 --------------------------------------------------------------------
Right click on the terminal of the listbox and from the context menu select create->reference. Then right click on the reference and click create->control. Copy the reference control onto the front panel of your subvi and after you have saved the subvi, drop it on the block diagram and wire the reference to it.