Print-Your-Own tickets are non-refundable. But if your ticket is for a Virgin Trains route you can make a change, for a £10.00 charge. You’ll have to keep the same route, but you can change the date or time of your ticket up to 18:00 the day before your train’s due to depart.
If you had a group booking and the lead passenger is named on all the tickets, any changes made to the lead passenger’s ticket will affect all other tickets on the booking. So, any unchanged tickets will become invalid.
If your group booking names each individual passenger on their ticket, then you’re free to change any ticket individually and it won’t affect the others.