They're creatively said — line's blown initially (2-4)
I believe the answer is:
ad-libs
'they're' is the definition.
The definition suggests an adverb but the answer is not.
'creatively said line's blown initially' is the wordplay.
'creatively' indicates an anagram (I've seen this in other clues).
'initially' suggests taking the first letters.
The initial letters of 'line blown' is 'lb'.
'said'+'lb'='saidlb'
'saidlb' is an anagram of 'AD-LIBS'.
(Other definitions for ad-libs that I've seen before include "Extemporary remarks" , "Improvises" , "Extemporaneous remarks" .)