I hope you can (haven't tried it myself), but:

• you need to have the image first (but thanks for reminding me, I will definitely make one before sending it in)
• pressing 'Reset' in the Settings is much easier (I can imagine that not everyone can handle dd or command line for that matter)
• what I'm suggesting is the officially supported method. Seeing how many people think it is a good idea to remove battery while the OS is upgrading just because they are tired of waiting - and then they are surprised that their phone doesn't work, I would definitely not fiddle with the backup partition if I were them and I would not accept the broken phone for a warranty repair if I were Jolla

So yeah, dd is good as the last resort, but my post was targeted at those people who need to send their Jolla for repair anyways and they do not want to end up with 1.1.9.28 flashed on their phone.


EDIT: Reading your reply again, you probably didn't get the point of my post I was talking only about warranty repairs and that the favor of them not flashing Sailfish 2.0 will be available only until the next release comes out. And that still stands.