You should be able to update the xFolderID by using UPDATE_DOCINFO service. Its part of the custom metadata list even though its specific to Records Management. If you are using the GenericSoapService then just add the xFolderID metadata as part of the request. In case if you are planning to use the WSDL from content server then create a new WSDL for update service and include the xFolderID as part of the data list.
It is posible tu update the xfolderid attribute performing a SOAP Web Service?
Yes, you can update it using webservice. Are you looking for a sample code for it ?