Newly re-enact entry as occasion for commemoration perhaps (12)
I believe the answer is:
tercentenary
'occasion for commemoration perhaps' is the definition.
'newly re-enact entry' is the wordplay.
'newly' indicates an anagram.
're-enact' becomes 'reenact' ('reenact' can be a synonym of 're-enact').
'reenact'+'entry'='reenactentry'
'reenactentry' is an anagram of 'TERCENTENARY'.
'as' acts as a link.
(Other definitions for tercentenary that I've seen before include "Three hundredth anniversary" , "celebration of historic event" , "Three-hundredth anniversary" , "Our observance now of Queen Anne''s succession, for example" .)