You can flash the first stage bootloader to remove that warning, but that is not documented well (if you can call several contradictory forum threads documentation), involves taking the laptop apart and gives you exactly one try: it either works or bricks the device permanently.
In addition to that, at least Samsung's Chromebooks are not very well designed and can be seriously damaged from userspace when running a general-purpose distribution (Google for burning speakers on ARM Chromebook for instance)