As you progress deeper in to Flying Stars Feng Shui, you'd discover that EVERY star (including the usually negative numbers of #5, #7, #3 and #2) can be positive or negative DEPENDING on situational factors and even including what business you are in. For instance, double #7s in the South are very different than double #7s in the North sector. In your case, there's no need to change to Period 8. Double #7s in the North are not considered negative in Period 8. Especially if you can tap to certain specific degrees within the North direction.
For beginners of course, these principles look pretty complicated. 8 Mansions and Flying Stars do not contradict each other. They operate on different levels and are used the property in different perspectives.
Warm Regards, - JY