Before moving too far forward with an amendment to a planning proposal it’s worth remembering that, in planning law, the status of a completed building often differs from that of a partially completed building. The following case in south Wales sets out a bit of relevant case law.
In this case an inspector upheld an invalidity notice (DCS Number 400-018-769), ruling that an application for an additional floor on a partly constructed student accommodation block must relate to the whole building rather than the revised elements only.
The council had refused to validate the application on the basis that the proposal represented so substantial a change to the extant permission as to constitute a new scheme. The essential difference between the parties was whether the applicant had to apply for planning permission for the whole of the main block. The inspector referred to Sage v Secretary of State for the Environment, Transport and the Regions and others  in which it was held that there is a distinction in law between a case where the building has been completed and is then altered and one where it has not been completed.
The inspector ruled that where a building has not been completed, an application which seeks to alter that building must take account of the entire building operation then proposed. He reasoned that such an approach is entirely logical; if planning permission were granted for part of a building which, if implemented, would result in a building different from that originally permitted and prevent the original building ever being completed, then the resultant building would clearly constitute a different development, not an altered version of the uncompleted original building, and should therefore be considered on its own merits. The appeal was dismissed and the notice of invalidity upheld.
Section 5.151 of DCP Online concerns the acknowledgement and registration of planning applications.