How to turn off System Update notifications?

[AC Question]

After previous forays into Lollipop & Marshmallow I've found that I *much* prefer to use KitKat -- particularly in that every notification I get stays neatly into the notification bar, and I don't have ever gchat message taking up a quarter of my screen in a white popup card.

So I now have KitKat on my Samsung S5 (SM-G900P, on Sprint Network). Problem is- the omnipresent System Update notifications telling me that the upgrade to Marshmallow has been downloaded & I need to give it the OK to install.

For many months now I've used Package Disabler Pro to block com.wssyncmldm & it worked great, but since Monday (12/12/2016) the notifications have returned. I cannot find what else to block with Package Disabler Pro.

I have tried long-pressing on the System Update notification to uncheck the "Show notifications" option for the Software Update software, but the box is greyed out and I cannot uncheck it.

I have also unchecked "Auto update" under the System Update options. But the notifications persist.

I've reached out to Samsung, Sprint, and OSP (they make Package Disabler) for assistance. Samsung and Sprint have both outright refused to turn off updates or help me to hide the notifications, both insisting that I must update to Marshmallow. OSP has not yet responded.

So...
Any further tips on how to get rid of the notifications?

 

[Rukbat]

The phone has to be rooted. Look in Application manager for an app with a name that has "update" in it. Disable that app (you may have to freeze it with Link2SD)

That way, if you ever decide that you do want to update, all you have to do is reflash the stock ROM (make sure you back up all your apps and data first).