If your client can handle WSDL files, then i would think that you dont need to change much. Becuase the SOAP message is defined within the WSDL, and if the client can handle WSDLs, then they will make the right SOAP messages according that your server-side code is expecting. All this is assuming that the client is "smart enough" to handle WSDL files.
Some clients, even thought they can handle WSDL files, can only handle a simplified version. So it depends on what the client is.
I suppose the only thing you have to worry about is the client sticks to an encoding (of the XML SOAP message) that the java side expects.
And another thing you might want to take care of is: interoperability issues with Web Services. Just so that your data doesnt loose itegrity when going from A to B.
Hope this helps,
- Web Services in 15 Minutes -