You could try something like this:
Warning: This may break in the future if the classes change. Also, it will leave the toolbar with the other 2 buttons rendered and it may break the usability of the product.
Depending on the use case, we may want to provide an API to access toolbar buttons. Could I ask what you are trying to achieve?
It would be great to have some control on the those buttons. In many cases we hide "Save and New" button because in the context in which a new record is created, doesn't allow a (second) new record. For example a person can have only one drivers license.
Also we rename the "Save" button a lot in status change pages. This because (our) users have trouble to relate the save action to a workflow action. They find it better to understand to name the save button in relation to the action they are performing. For example the users wants to mark an task as complete. The text: "Complete task" better describes the action then "Save".
At the moment we use scripting to rename the buttons, but it would be better to have a structural solution for this. Also like you mentioned the scripting solutions might break in future releases.
I have created a nice grid that have two buttons. the first is "Load Students" which populates the grid and the second button, "Save Attendance" which uses scripts to save the attendance record and there is no need for the Rollbase Save Button:
· Show / hide buttons
· Provide custom labels ( and their translations? )
· Re-order buttons?
· Keeping responsive in mind, you also may want to provide hints about always-show, always-overflow