any return in respect of an ‘affected transaction‘ may be amended (within the period allowed for amendment of that return) to take account of that election
caniateir diwygio unrhyw ffurflen mewn cysylltiad â ‘thrafodiad yr effeithir arno’ (o fewn y cyfnod a ganiateir ar gyfer diwygio’r ffurflen dreth honno, er mwyn adlewyrchu’r dewis hwnnw.