Export mappings always export to UTF-8. As long as you use only ISO-8859-1 characters in your application, the result of the mapping is an ISO-8859-1 string. It just has the wrong encoding declaration. If you replace the UTF-8 encoding declaration with iso-8859-1, the message should be accepted by the SOAP service.
So try the following:
That looks something like this:
Have you discussed this with the implementation side? Why are they removing support for UTF-8? This is a default encoding that should be supported by all webservices.
According to WS-I Basic Profile 1.0 the xml parser used by a webservice needs to support UTF-8: http://www.ws-i.org/profiles/BasicProfile-1.0-2004-04-16.html#refinement16457984.