Thank you for the nice words!
There is a code library of how to programmatically changing the context menu depending on the selection:
Changing context menu programmatically client-side. The sample provided there will help you implement your scenario via the provided ability to get access to the context menu and manage its items.
As for removing items from the built-in context menus please check out this article: Context Menus Overview. It shows how to predefine the default context menus.
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