Reason to be upset following small change in role (7)
I believe the answer is:
persona
'role' is the definition.
(I know that role can be written as persona)
'reason to be upset following small change' is the wordplay.
'to be upset' is an anagram indicator (I've seen 'are upset' mean this).
'following' is a charade indicator (letters next to each other).
'small change' becomes 'p' (short for pence).
'reason' with letters rearranged gives 'ersona'.
'ersona' after 'p' is 'PERSONA'.
'in' is the link.
(Other definitions for persona that I've seen before include "Public image" , "Assumed identity" , "No pears (anag.)" , "One who is diplomatically acceptable" , "Role adopted by actor" .)