Unfortunately the Roon Rock (Linux) Core has hidden (and encrypted) system files. Same with my Nucleus. No way to change the display_ui. And even if that was possible - every update would overwrite the individual changes made.
It works for the Roon Core running on Windows … but WIN is not, what Roon OS was developed for.
Have a look at my thread from last year, some visualisations (and Comments from Roon 
) (User selectable) Alternative Designs for Web-Display