Insert,
Box, Custom
Box, Options, Edit
Use Edit Custom Box to modify one of the existing box styles accessible through the Custom Box dialog.
Note: The actions 2 and 3 are not available for the predefined box styles (Default Cell Box, Default Staff Box, Default Object, Default Text Box). However, editing the formatting options of those styles will affect the default appearance of the boxes inserted by the Cell Box, Staff Box, Insert Object and Text Box commands.