There isn't a big change here. It was felt that by changing the wording slightly, we would just be clarifying it:
That the Committee retain, as needed, the services of one or more analysts from the Library of Parliament to assist the Committee in its work. These services may be requested at the discretion of the Chair.
That's the only difference there. If the services weren't required, then the chair would have the opportunity to have input into that. That's the only difference.