If you log in during this event, you will immediately get sorted into a group whether you want it or not. This rule applies to both FM and HP. Although I don't immediately change my app, but if I spot an obvious cheater in my group, I'll immediately change my app. There's no use even if I looked like a regular player, if there's a cheater in my group, it will only need one contact support from one innocent player to put me at high risk.
You can participate in both event as long as you are prudent, respect other players, and be convincing enough. Many get banned even though they're already keeping low profile because they don't understand this game gameplay mechanics. I thanked the spreadsheet for this.