Attendants conceal idea - a change of opinion (6,8)
I believe the answer is:
second thoughts
'a change of opinion' is the definition.
I can't judge whether this defines the answer.
'attendants conceal idea' is the wordplay.
'attendants' becomes 'seconds' (second is a kind of attendant).
'conceal' is an insertion indicator.
'idea' becomes 'thought' (synonyms).
'seconds' going around 'thought' is 'SECOND THOUGHTS'.
Can you help me to learn more?
(Other definitions for second thoughts that I've seen before include "Change of mind" , "Change of opinion possibly" , "change of plan" , "Revised view" , "Doubts; reconsideration" .)