Hello Jan
I would suggest you ring the people in the main office they I am sure can point you in the right direction, or post on the editors board on here and Julia might be able to help you.
I have know of cases where people have had to cancel or change at short notice which sometime can be done, you might have to pay a changing fee or maybe you could just book the tour on a maybe you would be able to go...obviously I am not qualified to totally answer you so, If it was me I would talk to the girls..boys in the office they are usually most helpful.
It hope you can get the right answers and I hope you get to do the tour.
Cindy