Fictional millionaire just about manages with small change (6)
I believe the answer is:
gatsby
'fictional millionaire' is the definition.
'gatsby' can be an answer for 'millionaire' (I have seen 'Novel millionaire' mean 'gatsby' so perhaps 'millionaire' could also mean 'gatsby'). I'm not certain of the 'fictional' bit.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for gatsby that I've seen before include "Classic novel by F Scott Fitzgerald - 'The Great . . . . . .'" , "F Scott Fitgerald wrote 'The Great ......'" , "F Scott Fitzgerald wrote 'The Great . . .'" , "Great character in Fitzgerald novel" , "Fitzgerald's Great character" .)