Pass our flag (6)
I believe the answer is:
colour
'flag' is the definition.
The answer and definition can be both related to change as well as being verbs in their base form.
Maybe you can see an association between them that I don't see?
'pass our' is the wordplay.
'pass' becomes 'col' (col is a term for a mountain pass).
'col'+'our'='COLOUR'
Can you help me to learn more?
(Other definitions for colour that I've seen before include "Red or green, say" , "Blue or green, say" , "Such a sergeant" , "'Tinge, hue (6)'" , "Complexion - pretext" .)