I currently have the anniversary update on my L650 and do NOT want the creators update. To avoid this phone update is very simple...just NEVER turn Wi-Fi on.
That's right. When you go into "Phone Update" it states, "Available updates will be downloaded and installed automatically, EXCEPT OVER METERED CONNECTIONS (where charges may apply)". You must live without using Wi-Fi, so make sure your Wi-Fi is set to off, and "turn Wi-Fi back on" is set to manually. (Having an unlimited data plan makes this okay for me)
Just always know that if Wi-Fi turns on at all, the update to will download automatically.