I want know if it is possible to save shapes in “Lines and Arrows” so that can be readily accessed anytime. As an example, suppose I create coordinate axes for a particular drawing. Since the coordinate axes are so simple I wish to save them to Line and Arrows tools of LibreDraw. Please outline the procedure if it can be done.
No, that is not possible, because the items in “Lines and Arrows”-windows (and all the others) are actually no drawing-objects, but they are .uno commands.
The usual way to collect custom drawing objects is to make a theme in the Gallery and drag the drawings into the Gallery.
But for coordinate systems I use a different way. I draw the coordinate system in a new layer, set the layer to write-protect and then save that document as template, example.