EASA 21.A.91 - classification of changes and the associated AMC and GM:
https://www.easa.europa.eu/system/fi...2012-020-R.pdf
There is no 'Form/Fit/Function' replacement without approved data under EASA other than use of PMA parts, and even then, only when the part is non-critical and the specific EASA aircraft type is listed on the component PMA approval.