in libreoffice writer is it possible to customize context menus?

I’d like to be able to “Select All” with a mouse right click, instead of using ctr + A
Is it possible to edit or add to the context menus?

You can place the Select All icon on the Toolbar.

Right click any icon on the toolbar.
Click Visible Buttons

The option to customise context menus will be available in 5.2, due for release in August.