It seems to be the case that with these blockades, Network Rail are paying for additional agency staff to be at stations affected by the blockade. Trowbridge and Westbury have at least three additional agency people at each station to supervise one bus every couple of hours! Although wearing GWR▸ uniform, they are agency staff with (understandably) a limited amount of operational knowledge.
I have been astonished at the level at Trowbridge - perhaps I caught them on a protracted shift change, as I counted six of them. Yes, for one bus every couple of hours.
Personally, I feel they would be more useful if split between the stations they're at and Melksham, which is normally unstaffed, but where there is no alternative timetable on display. The normal 18 trains a day are cut to a reduced schedule of 7 (some at different times to when there are normally trains), plus 9 bus calls (yes, less services in total), and the seven trains have proven to be very unreliable indeed - cancellations even from that reduced schedule on most days. Having a member of staff there, even with limited knowledge but knowing who to phone up and how to find out what's going on, help with alternative plans, and re-assure would be a far better investment than clumping staff where there are GWR staff anyway.