Sprint didn't do much other than add a few extra icons for suggested apps to install and the new 3G/4GLTE icons to match the brand. Those were probably in response to the blandness compared to it's competitors and the previous 4G WiMax. I told support up front I changed my icon to VZW's just because it said LTE then found out this broke Google wallet, LoL.
You can't access Knox directly. It's like parental controls from a bigger parent. In some cases, it even trumps SU permissions which is annoying. I have to find a Knox compatible SQL editor to add my toggles back to Settings.db since SQLite Editor is blocked by Knox. You won't really interact with it much as long as nothing makes it angry. XDA has already found a way to remove Knox.
As mentioned, most of the changes are under the hood for the general populace. You can see a few new apps added to the System layer just by going through your Play Store's installed apps list.