To amplify what Jet Ranger said:
FCL.710 Class and type ratings — variants
(a) In order to extend his/her privileges to another variant of aircraft within one class or type rating, the pilot shall undertake differences or familiarisation training. In the case of variants within a type rating, the differences or familiarisation training shall include the relevant elements defined in the operational suitability data established in accordance with Part-21.
Compare and contrast with a similar statement with regard to, say, class or type ratings:
FCL.725 Requirements for the issue of class and type ratings
(a) Training course. An applicant for a class or type rating shall complete a training course at an ATO. The type rating training course shall include the mandatory training elements for the relevant type as defined in the operational suitability data established in accordance with Part-21.
Notice the difference?