And if you open it up and unplug the battery, then boot off the charger that disables the write protect and you can install actual linux, though a lot of chromebooks have unique hardware that might not be supported, particularly audio IME.
I used to have a dell chromebook 11, and with bitmap fonts it was actually a pretty slick little computer for <$100.
Depending on how old it might be another method. Some have a switch somewhere, or a specific screw. Check out mrchromebox's page.
And yeah you just boot it with the battery disconnected once and it disables the write protect!