uninstallation - Reinstall System app which is uninstalled for the current user?

So, I have already posted this on reddit, but I might reach a better audience here.
I "uninstalled" google play games using this guide by XDA. Now I need to reinstall it. This is the command, how I should be able to reinstall the app: adb shell cmd package install-existing
But there is one problem: My phone is on Android Lollipop, and the command doesn't exist there. I manually tried to install the apk back, with adb and with normal package installer. The Settings app always says something like Not installed for user" (translated from other language).

So I have 2 Questions:
1) In which Android version was this command introduced?
and 2) How can I get this app back?

PS: I have root access, but would prefer a non rooted solution.