When the certificate has expired, a new certificate has to be issued under the new name of the company. If the certificate is still valid and only the name of the company has changed then you may just amend the previous certificate by updating the name. However, all these processes should be clearly defined in your NSA’s internal procedure.
Updating the name of an international railway undertaking might have an impact on all certificates the railway undertaking has. In some cases, issuing of a single safety certificate will be required which means that a railway undertaking will need to demonstrate compliance with the new SMS requirements.