Extend XSD to put individual elements instead of using the xs:any in an XSD

I have an XSD with an xs:any This allows me to insert any tags/elemnents of my choice. However, I would like to extend this XSD so that instead of using xs:any, I can specify my own specific elements.

I do not want to edit the same XSD but create an extension XSD that adds speeicifies the specific elements I would like to use instead of using xs:any

Here is a part of my XSD.

...
...
... 
<xs:element name="MRegReq" type="mss:MRegReqType" />
<xs:complexType name="MRegReqType">
    <xs:complexContent>
        <xs:extension base="mss:MessageAbstractType">
            <xs:sequence>
                <xs:element name="User" type="mss:UserType" />
                <xs:element name="EData" type="xenc:EDataType"
                    minOccurs="0" />
                <xs:any namespace="##other" processContents="lax" minOccurs="0"
                    maxOccurs="unbounded" />
            </xs:sequence>
        </xs:extension>
    </xs:complexContent>
</xs:complexType>

In the above,

is what I would like to replace with an extension, so that when I regenerate the stubs etc using JAX-WS, I can get access to the individual elements specified in the XSD extension (instead of having to get the request.getAny() and iterate through the nodes to get each element).

Any pointers/help would be really appreciated