writing file creation date to tag with this format : YYYYMMDD (year, month, day)

Support
2

%_file_create_date% gives you DD.MM.YYYY not DD/MM/YYYY

$regexp(%_file_create_date%,(..)/(..)/(....),$3$2$1) gives you YYYYMMDD like you want it.

Edit:
How to write it into a tag:
Action: Format Value
Field: YEAR
Format String: $regexp(%_file_create_date%,(..)/(..)/(....),$3$2$1)