What is a one-sentence summary of the following article?
If you've been given the go-ahead to expand your role into the new areas, ask that human resources formalize this by way of a new job description. This will ensure that the new activities and the role expansion are officially recognized and become an expected part of the workplace routine. It also allows the role itself to become more desirable and to have ongoing value when you get promoted later, leaving your expanded role as a real position for someone else to step into at a later stage.

Summary:
Request formalization of your new role.