compare the new generated WSDL against the old and be very careful
Okay, in that case without necessarily needing to know which approach has been used so far, you can do in either way
Public registries have pretty much been a failure, not a single one worth mentioning remains in existence today.
This makes sense, if I presume the service provider is using some XML parser to read your request SOAP message than standard Web Services API.
Otherwise, if the response SOAP message is not a valid SOAP message then use any XML parser to read it.
The details about using this service should be provided to authorized users from the owners of the service
Humans can typically read a WSDL file in a browser for reference purposes, unless there are implemented security mechanisms to prevent this.