No, after a PoS has been issued by the producer of the final biomass fuel, it may not be modified anymore. This means that the sustainability characteristics related to the batch of biogas/biomethane (e.g. feedstock composition, GHG value, country of origin) are fixed for the dedicated batch of biogas/ biomethane. It is possible to collate or group multiple PoSin one file using other formatting than that in the ISCC templates. In this context, it is important that traceability is maintained and that all information present on the initial PoS is retained and e.g. the GHG values are not recalculated. Please see the lastest version of ISCC EU System Document 203 “Traceability and Chain of Custody” (chapters 3.4.8 and 3.4.9).