The examiner may then sign the new rating on the front of the licence.
Only if specifically authorised by the UK CAA. I had my wrist slapped for signing an Irish licence.
IN2015-50
6.2 Unless specifically authorised by the UK CAA, examiners holding Part-FCL examiner certificates issued by countries other than the UK are not permitted to endorse the certificate of revalidation of a UK-issued licence. Where the examiner notifies the intent to conduct a proficiency check or assessment of competence in accordance with the procedure under paragraph 4 of this Information Notice, the e-mail from the CAA confirming notification will include an authorisation permitting the examiner to endorse the revalidation page of the licence. This authorisation will be valid once only and will be for the specific renewal/revalidation of the qualification for the particular licence holder being examined.