One trying to change baby in Istanbul? (5,4)
I believe the answer is:
young turk
'one trying to change' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'baby in istanbul?' is the wordplay.
'baby' becomes 'young' (similar in meaning).
'in istanbul?' becomes 'turk' (I can't explain this - if you can you should give a lot more credence to this answer).
'young'+'turk'='YOUNG TURK'
Can you help me to learn more?
(Other definitions for young turk that I've seen before include "Rebellious party member" , "impetuous individual" , "one's anxious to change" , "Baby in Izmir" , "Rebellious person of immature years - from Ankara?" .)