I just made a sample plugin and attached, you can directly import zipped plugin into SailPoint. You can customize as per requirement for disabling the button.
To learn more information about plugin, here are some helpful link. There is To-do plugin which can be more helpful for a reference.
Thank you very much for your Plugin example using Javascript to mask the forwarding button. I can build on your example. I also appreciate the pointers to developing plugins.
I need to research how to mask the forwarding put for select forms only.