Prevent Accidentally Editing Shape-Keys

Can anyone make this? Or let me know how I would get started on implementing this myself via addon or something? (P.S. I use Blender 2.79 cuz 2.8x doesn't work)

PROBLEM: Sometimes, I want to edit a mesh's basis shape-key. But I forget I had shape-keys. So I accidentally edit a non-basis shape-key. This causes annoying issues. Not sure I can even salvage a ruined shape-key in a practical way. I wanna use shape-keys, but this makes it hard.

.......

PROPOSAL: Is there a way to make the background in 3D View change colour whenever I edit a non-basis shape-key? That way, it'd be obvious when I'm about to accidentally edit a non-basis shape-key. It doesn't have to be changing the background colour. But it has to be super-obvious so I don't forget I have shape-keys when I want to edit my mesh's default basis shape-key. I once tried making selected vertices the 'default' vertices, but iirc, the solution I found was confusing and didn't really work.

.......

P.S. I use Blender 2.79 because 2.8x doesn't work on my laptop. If u can, feel free to make this for Blender 2.79 as well...? Or an addon? Or let me know how I can get started on doing this myself...

P.P.S. there's no tag for shape-keys.