In the
NRCoC it says:
19. Using a combination of tickets
You may use two or more tickets for one journey as long as together they cover the entire
journey and one of the following applies:
(a) they are both Zonal Tickets (unless special conditions prohibit their use);
(b) the train you are in calls at a station where you change from one
ticket to another; or
(c) one of the tickets is a Season Ticket (which for this purpose does not include
Season Tickets or travel passes issued on behalf of a passenger transport
executive or local authority) or a leisure travel pass, and the other ticket(s) is/are not.
You must comply with any restriction shown on the tickets relating to travel in the trains of
a particular Train Company or Train Companies (see Condition 10).
If you do not comply with this Condition, you will be treated as having joined the train
without a ticket and the relevant parts of Condition 2 or 4 will apply, either to the entire
journey, or from the last station where the train stopped at which at least one of the
tickets was valid.
For the purposes of this Condition, a “leisure travel pass” means any multi-journey ticket
(excluding Season Tickets) valid for:
(i) at least 7 consecutive days; or
(ii) at least 3 days in a period of at least 7 consecutive days
and includes rover tickets, travel passes, flexipass tickets and Britrail passes.
I've bolded the important bits. By my reading of that both of the Freedom of the North East rovers meet the condition of being a leisure travel pass therefore you could buy a Berwick to Edinburgh return ticket and use it in combination with the rover even if the train you're traveling on doesn't call at Berwick.
