Article 4.4 of the Framework Regulation for Energy Labelling (EU) 2017/1369 reads:
4. A product for which changes are made that are relevant for the label or the product information sheet shall be considered to be a new model. The supplier shall indicate in the database when it no longer places on the market units of a model.
If the energy label class changes because of modifications changes of the product, then the supplier must register the product as a new model and calculate the updated energy class. The supplier can create a new model with the same protocol and add an appendant, e.g. a '-V2' or '-1' or '_x' or '-[year]' to the model identifier. For the products already placed on the EU market and present in shops with an outdated energy class, the supplier should set in EPREL for that model the date of end of placing on the EU market.
Changes to existing registrations are instead allowed for these reasons (and do not require the supplier to make a brand-new registration):
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.