Under the Code of Practice for Celebrants, your Celebrant if requested by you, will conduct a rehearsal at a mutually agreed time, date and place. However, please remember that in this case, your Celebrant is entitled to charge an additional fee for this service: a fee which should be outlined in his/her "Statement of Fees" and discussed with you at your first meeting.
In many cases, having a simple run-through of certain aspects of your ceremony with your Celebrant, as opposed to a rehearsal, at your Celebrants home or office may not necessarily attract an additional fee. Again, this can be discussed at your first meeting.