Just saw your question so I thought I'd add a couple of observations.
The last arrival each night shunted and was berthed in P5 at Central overnight, (the bay behind the country end of the main down platform which is not signalled for passenger use), then forming the first train the next morning.
AFAICT▸ from
RTT» the
SWT▸ 444 that would normally berth there overnight was switched to Northam depot for the week.
During the middle of the day, as seen on Tuesday and Wednesday, the
GWR▸ departures and arrivals were using the country end of the island platform, P2B or P3B. Arrivals and departures were at the normal times, i.e. around about xx10, and there were clearly a few passengers for the departing service each time who were in 'automatic mode' and waiting at the A end of platform 4, where the trains normally go from. Staff appeared to be proactively looking for people in the wrong place, but the trains weren't necessarily held for latecomers appearing at the barriers nearly at departure time expecting to find them at the normal platform.
Following the down train's departure, the recent arrival each time was shunted via one of the loops west of the station to layover in platform 5, with a similar shunt made about 40 mins later to get the train back onto a public platform.
There was a certain amount of confusion just before 1500 on the Tuesday, as an earlier arrival at 1435 ish, the curtailed Gt Malvern to Brighton incoming train was sat at P2B awaiting its
ECS▸ path to Salisbury.
So a few people were approaching it to try and get on, thinking it was going to form the 1510 Cardiff departure, and there was clearly some worried passengers waiting and watching as it departed empty at about 1455, however the unit for the 1510 was also on its way, and arrived into the same platform from the west a few minutes later.
The oddest feature of the temporary workings was that the Great Malvern to Brighton train terminated and then ran empty all the way back to Salisbury to berth in the east sidings there until later in the evening, when it formed a Southampton Central to Bristol service in the path of the train normally originating from Brighton. Seems odd that there was nowhere nearer to stash a single
DMU▸ for a few hours between departure and arrival, but I guess driver route knowledge would be part of it...
Paul