Good luck with that...
I think there's some over thinking going on. The Cloud/ Server version will always 'win' in any situation where the cloud time stamp is more recent than the local version. Your local app will always ask: "is this note 'last changed' date earlier than the cloud version?" If the answer is 'yes', it gets replaced.
I keep a full local backup history of my notes because I can restore individual notes and notebooks in case of issues - the 'restore' in my (Legacy) case being an import to my database that will allow me to "update" a note/ notebook with missing or corrupted data. I've maintained a backup for as long as I've had an account with Evernote, because that's just good IT practice. I've had to use it once or twice in 12 years - and that was just to install Evernote on a new machine and replace that empty database with my own data. Evernote's server then runs a check on note dates, but doesn't replace any where the 'last changed' dates are the same - a much quicker process than downloading the whole database when you have over 50,000 notes...