Probably the plan all along. Although they got lucky and have a forecast with rain chances to give them cover for this.
I lived in NC not more than 20 miles from the location of the Stadium. In the summer and fall EVERY single weather forecast without exception contains these words,”chance of afternoon and evening thundershowers”, The only thing which will change is the % assigned to the chance of showers. As an example the forecast for Thursday is a 30% chance in the afternoon and a 20% chance in the evening and that is about as low as it gets.
The change of venue was for one reason, they could not fill the stadium. Unlike in the past they would not be able to fake it with camera angles because to many people are there with their own cameras.