To know the names of the components, you'd need to switch to the XML view in studio page tab. It'll show you the names of all the components on that page.
As long as you use that custom REST endpoint in the context of the page, rather on the same page where the default component is being used, you should be fine. E.g. if you use a blog page component on home page, you'll get an exception.
Thanks for the hint with the XML view!
The custom REST endpoint is getting used outside of the Lithium application itself, so I guess this would mean it doesn't work?
So that's the only solution? This is exactely what I wanted to avoid..
