Carol happy to change? That's questionable (10)
I believe the answer is:
apocryphal
'questionable' is the definition.
('apocryphal' can be similar in meaning to 'questionable')
'carol happy to change?' is the wordplay.
'to change?' indicates anagramming the letters (I've seen 'to change' mean this).
'carol'+'happy'='carolhappy'
'carolhappy' anagrammed gives 'APOCRYPHAL'.
'that's' is the link.
(Other definitions for apocryphal that I've seen before include "Fabulous" , "probably made-up" .)