How to drop 230V AC TO 200V AC
One way to do this is with another transformer. A 230vAC:30VAC connected to oppose the voltage will work. However you could also replace the transformer since it is only a small (12VA) transformer.

If you are trying to adapt a Japanese standard product to 230VAC you may find that there are primary taps on the transformer that you can use. 

Using a resistor is not a good idea generally because the voltage drop will vary with loading.