AutoLoadNotationPalette is a boolean variable. If
False then the Notation palette will not be loaded when the Notation package is loaded. If the value is undefined or
True the Notation palette will be loaded when the Notation package loads. Other package designers can set this variable outside of the Notation package through a statement similar to
Notation`AutoLoadNotationPalette = False.
So, to prevent the palette from loading you can simply use:
Notation`AutoLoadNotationPalette = False;
To close an already open
Notation Palette you can use