Unity3D Sprite ... but single sided?

As far as I'm aware, neither of these changes have any effects other than the that which you intended. Also, this is the most correct way to achieve this- it's the only thing Cull is for.

That won't cause any problems and is the correct way of doing things. If you want to be really explicit about it you could change the line to Cull Back instead of commenting it out, but back-face culling is defined as the default behaviour so just removing it is fine.