A little idea which came to mind today:
FileMaker 11, 12, 13, 14 and 15.
As you see we put a custom label and image on the toolbar items for delete and add record buttons.
You may know that we can create our own toolbar buttons. But we can now also modify existing toolbar items. You can now tell the plugin to keep an eye on the toolbar items which FileMaker uses. And when the plugin sees a FileMaker button being created, it can put a modified label on the button. Enjoy!
PS: You can even use triggers to setup this before you open a new window, so the new window will use the customized icons/labels.