It seems like you wanted to add some more controls to RTE if yes, You can easily add and remove RTE controls based on your requirement, In RTE component you will have two nodes named rtePlugins and uiSettings respectively, these two nodes can be used for the same purpose.
I have gone through the documentation. But unable to find somethin for my problem. I want to add a button inside rich text. So no plugin for that right ? So when achieving it on custom way can you guide me little more ?