Yes. You may edit, add or remove products and people included in your booking up to two days prior to the start of your scheduled rental period. This also applies to your companions.
In other words, you may wish to add people to your group or, for example in the case of illness, remove them. If you are forced to remove someone, the difference in cost will be refunded to you using the method you chose for your original payment. If you add a person, you will be able to pay the additional amount directly online.