Basically, it's a shopping list that has a note added, saying "Hopefully you won't forget it this time, Daniel." The shopping list itself is completely indestructible and can't be edited. Anyone who reads it memorizes it instantly and permanently. When someone copies the text onto something else, the new thing also becomes an instance of this SCP and becomes indestructible and uneditable as well, even if it's on a computer. This only works if it's copied down word for word. They find out later that the two effects are actually the same, after someone who's read it dies and a small part of their brain remains even after they're cremated. They keep doing research on it and discover that there's a single line where they can put whatever text they want, and it'll also become permanent/memorized. This is also where they find out the SCP overwrites random information if there isn't enough room for it. Again, this applies to human brains.
There could also be an incident report where an instance with a very long editable line gets out and ends up giving people seizures, amnesia, etc.
That's about it, I hope it wasn't too long. Please let me know whether or not you think this is an interesting idea, or what I could add/remove.