Well I have now needed to use it and it worked like a dream - ticket changed in less than a minute and at no cost.Cross Country state they do but I have never needed to test it.
Change Advance Train Ticket without an Admin Fee | CrossCountry | CrossCountry
We've made it free to change your Advance Train Tickets for added confidence and flexibility when booking with CrossCountry Trains.www.crosscountrytrains.co.uk