Do you have to stick to the strict guidelines or Prince2 or can you be flexible and adapt it to your specific project?

PRINCE2 can be adapted to your specific project; in fact the methodology is designed to be flexed and tailored to any project regardless of the size, type, organisation, or culture - it is a framework that can be scaled up/down to suit. 

Prince 2 is a flexible framework and it can be tailoring to any project environment regardless project culture, nature and size.

Prince2 should be tailored for each organization, it can be shaped to Agile programing or any specific project methodology.

Ofcourse there will be flexibility and alternates, though limited, in order to suite specific needs.