Under option C if there is a removal of scope I would usually raise a negative CE to reduce the scope.
What about option A? The job was priced as a lump sum, however a section of scope is being removed by the client. Should a negative CE be removed to reduce final cost? Or as it was lump sum project should that be the final cost?
If there has been a CE to reduce the scope, and provided that the core clauses have not been amended, then a negative compensation event should be assessed to reflect the saving in Defined Cost + Fee of not doing the work (considering any change in risk profile etc).By agreement the saving/reduction could be based on something else.
Under Clause 60.1(1) a change to the scope (which is still called the works information under NEC3, and will only be called the Scope under NEC4) is a compensation event with only two exceptions as noted in that clause. The change still constitutes a compensation event irrespective of whether it adds cost or time, reduces cost or time, or is ultimately determined to have no effect on either, so the PM should always notify a CE for any change to the WI, irrespective of the particular main option.
The clause Dave points to below is option A clause 63.14. Note rates and lumps may only be used AS A BASIS by AGREEMENT !