Can I extend our itinerary or trip after reaching Bhutan? What about the Visa extension in such cases?

Yes, you can extend your stay, even upon reaching Bhutan. All extension of itinerary means an extension of trip in Bhutan and in such cases; one pays the full tariff on the actual number of nights extended plus a Visa extension fee. The visa is then extended for the actual number of nights extended in Bhutan.  However this will be subject to available flights and rooms at that time.