Specifically to change the order of the buttons and to remove some? The documentation describes how to add menu items and toolbar buttons, but nothing else.
You could try adding a custom privilege to a menu item, and restrict which users have access to that menu item. See the "OneClick Customization" document - Creating Custom Privileges. (https://docops.ca.com/ca-spectrum/10-2-1/en/customizing/oneclick-customization/creating-custom-privileges).