I've attempted to formalise how I think this should be approached by the industry. If this were followed, then it might make signallers/control think twice about enacting certain last minute changes. Let me know your thoughts...
Each station should have a matrix of travel times between pairs of platforms in the station. The travel time between a platform 'P' and another platform 'Q' will be deonoted as P~Q.
If a station has a concourse area, then this can be deonted by Ĉ, or Ĉ1, Ĉ2 etc. where there are multiple concourse areas. These concourse areas should also feature in the station matrix, for example, the travel time between concourse Ĉ2 and platform Q would be deonted as Ĉ2~Q.
In all cases, the values in the station matrix should assume that a passenger is having to move from the furthest end of their original platform/concourse, to the furthest end of their new platform. It should also be set on the assumption that a passenger travels an average of 1m/s to ensure fairness for people with limited mobility and to allow for crowding/general confusion!
A station's minimum connection time will be equal to the highest number in the station matrix and this will be denoted simply as ~.
SCENARIO 1 - PLATFORM ALTERATION
If a train's platform is altered from platform P to platform Q, then the train may depart on time provided there is ample notice of this alteration. The required notice is the corresponding value from the station matrix, P~Q. However, if the platform alteration is announced X minutes after the P~Q minute deadline, then the train must be delayed by X minutes and the station displays must be updated to reflect the new expected departure time.
SCENARIO 2 - PLATFORM SURPRESSED
If a train is not yet ready to be advertised at a station at ~ minus X minutes before its scheduled departure, then the train should be delayed by X minutes and the station displays should automatically update the expected departure time to reflect this.
However, if passengers are explicitly told to wait in a certain part of the station (e.g. concourse 2), then a train only needs to be advertised Ĉ2~Q minutes before departure (i.e. the value in the station matrix for the time between concourse 2 and the far end of platform Q). Still, if a train's platform announcement is delayed X minutes past the Ĉ2~Q minute deadline, then the train should wait until X minutes after its scheduled departure to leave.