A policy, by definition, is a set of principles or rules that are implemented for the purpose of obtaining or reaching a particular outcome or goal. Therefore, policies, in essence, exist in a variety of endless contexts.
Though a policy may be implemented for a particular time achieving the intended purpose, it may prove necessary to amend or revise a policy. Revising a policy can take various routes.
Revising a policy will usually be at the discretion of the entities or parties that implement the policy in the first place. In devising a policy, it is common that procedures in the changing or revising of the policy be included for future reference or circumstance. Each individual policy that exists and the actual actions or procedures involved in revising a policy will differ in accordance to the needs of the faction or party and the changes that are to take place.