Procedures are established to allow for these modifications if proposers consider there is a need to modify and refine approved observations after the call has been closed. They intend to allow some flexibility if the changes are oriented to maximise the scientific return of the mission. However, they will be restricted to the minimum, reviewed and approved by the HSC Community Support Group and requested through Helpdesk.

The modifications made shall not alter the scientific content or intent of the original AOR and must be such that the programme stays within the originally allocated observing time. Major modifications will need to be reviewed and approved by the Project Scientist, in consultation with the HOTAC, if necessary.

In cases where changes of the expected/verified in-flight performance of a given instrument or observing mode will result in seriously degraded scientific results for a given proposal (or a subset of proposals), the HOTAC may be consulted to evaluate the new observing conditions and take necessary actions.