As Norman indicates, the Probation Service can amend the terms of a licence since the over-riding condition of any release licence is that the offender should comply with all reasonable requirements of the Probation Service. A decision to change the terms of a licence can only be challenged, through the courts, on the grounds that the Probation Service have acted unreasonably in amending the terms of the licence.
For example, someone might have a licence condition that they can't go within 1 mile of the home of Ethel Bloggs. If the Probation Service later realize that Ethel works on an Asda checkout, and the person on licence might shop there, they could reasonably impose an additional condition preventing him from entering that branch of Asda. However, if they changed the licence conditions so as to ban him from all Asda stores, the decision could be overturned, on judicial review, on the grounds that it was unreasonable.
Chris