I don't need necessarily to have the wording changed, as long as there is something understood. Normally a vice-chair would sit in on a meeting or cover one or two meetings at most, but I had a situation with the health committee last year when the chair was absent for an extended period of time, and we had a vice-chair.
As long as the last sentence here, “These services may be requested at the discretion of the chair”, is understood to mean whoever is sitting in the chair, then I'm fine, as long as there is that understanding.