Risk is a given in any investment. It is incorporated into valuation in the cost of equity and debt which flows into the discount rate. International projects are considered higher risk given the potential for political and/or currency fluctuations. Therefore a risk premium is added for international projects.
The factors that influence country risk premium change as time passes by. Therefore the country risk premium does get revised. Frequency really depends on the magnitude of change. Significant changes can require immediate changes. For example, war, overthrowing of a democratic government or a revolution causes overnight changes.