Chilled American airport involved in grass (7)
I believe the answer is:
relaxed
'chilled american' is the definition.
The answer and definition can be both related to change as well as being past participle verbs.
Perhaps you can see an association between them that I can't see?
'airport involved in grass' is the wordplay.
'airport' becomes 'lax' (abbreviation for Los Angeles International Airport).
'involved in' is an insertion indicator.
'grass' becomes 'reed' (I've seen this before).
'lax' inserted into 'reed' is 'RELAXED'.
Can you help me to learn more?
(Other definitions for relaxed that I've seen before include "Easy-going" , "Took it easy, loosened up" , "Without strain or anxiety" , "Unstressed" , "Without tension" .)