Read the whole thread now.
To your question on how to enhance a BSP component, check this:
How To Enhance a Web UI Component in SAP CRM - CRM - SCN Wiki
After you enhance the view that you need, you have to basically call your RFC in the place where edit button is instantiated in the view (it may either be a one click action, or in get_buttons or do_prepare output or a combination of these). There, do the RFC check and based on the result hide/show the edit button.
You could also consider making your code more efficient by calling the RFC only once when the view is loaded, for example in do_init_context and holding the value for checking the button instead of making the RFC call on every roundtrip when the button logic is triggered.
Regards,
Parul