Dear Siam,

I am afraid there is no easy way to change the spread since the historical data that is used with SphereTester contains the bid and ask price so it is not something that can be modified by the tool.

However, you can manipulate the historical tick data in excel to change the spread.
See this link to know more about the historical tick data – http://www.spheretester.com/user-guide/#Historical_data

if you need any other help, do not hesitate to contact us.

Thanks,
Aayush