Crediton, although about the same age as Exeter PSB, is a small self-contained western region 'E10K'* installation with a local relay-based interlocking and panel. A major issue at Exeter has been the 'panel processor', an old processor-based system that provides the multiplexed control links and handles the controls and indication logic for the wider remote-controlled areas overseen by Exeter such as Taunton and Newton Abbott, but not the immediate environs of Exeter St Davids, Cowley Bridge Junction and Exeter Central station which were provided with traditional relay-based panel circuits and direct multicore cable links instead. The panel processor supplier almost immediately ceased supporting the product, and that has prevented any reconfiguration requiring data changes, effectively locking in the current track layout for four decades! For example, the new properly signalled passenger connection to the West Somerset Railway had to wait until the level crossing at Silk Mills had been decommissioned, so the channels used for its manual control from Exeter could be reassigned to the new signalled routes without a panel processor reconfiguration being required. The panel processor issue would not affect any work at Crediton.
Although getting on for 40 years old, the existing installations' comparative simplicity at Crediton means some minor reconfiguration to accommodate a new method of block working replacing the train-staff to Okehampton is probably feasible, and that wouldn't require any track layout changes. Any more ambitious work to relocate crossovers etc would be best combined with a more ambitious resignalling scheme. As far as track renewals are concerned the PW costs for a new pair of crossovers near Yeoford would be little different to replacing them in situ at Crediton itself, but clearly the signalling changes for that would be rather more significant. My advice would be to bundle the track and signalling renewals together and combine these with an enhancement scheme to move the pointwork as desired and also change the method of block working towards Barnstaple. The overall 'SEU count'* of such a project should not be any more than a pure like-for-like renewal of the existing layout, thus should represent good value.
*E10K: E10,000, the master drawing number for a book of standard relay circuit diagrams used by BR Western Region signalling designers at Reading. They show annotated typical use-cases that can be customised for individual applications.
**SEU: 'signalling equivalent unit', a rough high-level estimate of size and complexity for signalling installations and projects. Each individual turnout and signal within an area being analysed adds a unit to the area total for the installation or project.