According to GS1's GTIN allocation rules for the Healthcare sector (find the explanatory article here), a change in packaging to add a new certification mark or to remove an existing one that has significance for competent authorities, notified bodies, other economic operators, and/or for the end consumer, therefore requires the allocation of a new GTIN.
However, it should also be noticed that when a certification mark is added to allow for sale in a new country/market, it has no impact on the countries/markets where the product was previously sold - in this case there is no need to assign a new GTIN in the above scenario.
Brand owners are responsible for the internal control of their inventory and any return systems. It is important that these systems, as well as the logistical management of phasing-in and phasing-out, can distinguish between "old" and "new" product. Where this can be achieved effectively by using an alternative identification satisfactory to all trading partners, a new GTIN need not be assigned in this scenario, but the external supply chain should not be affected in terms of expected functionality.