First, you must have version 4.8.2 installed (just replace it in /system/app with the new com.android.vending.apk)
Download a root service from the store called “Disable service” (again make sure root is installed and the app is given root permission)
Now, in the disable service app, navigate to the system app tab and find Google play store. Tap on it and you will get a list of services
Scroll to the bottom and uncheck “check Wifi And Update” service.
You will see a “please wait” notification, and at the bottom busybox should appear, notifying you that the app was given root access
Exit the app and voila! Google play store will never update itself or Google play services ever again (unless you install a new version, in which case you would need to repeat the process)

How can I stop Google play from automatically updating?