Just wanted to share this in case someone else finds it useful...
I have a rooted V7, and just wanted the update nag to stop. For a time, the nag went away, which I think was due to a bug in google play services. A subsequent automatic update brought the nag back and renewed my interest in getting rid of it.
The version checking relies on values in /system/build.prop. After taking a backup, I replaced the v7 build.prop with the v8 version (which I extracted from a v8 zip someone had posted here), and (once making sure permissions were 0644) that turned out to be sufficient to stop the nagging.
I may play with applying the other changes in the update (minus replacing the boot and recovery images) but I also may run out off free time before I get to that.