IsReadable keeps changing back.

I have had to set Is Readable on some textures because I actually use pixel information for other stuff.
When I do this, it seems happy for that session, but as soon as I leave Unity, it resets back to off on next load.
I saved the scenes and project.
Am I missing some apply permanent type property or something else?
Is there a way turn it on at code level?

Grumble. Found the Enable Read / Write setting further up. (Saw it, but the write part messed me up.)