Thank you for your answer.
Now I have a rpc, looking like this:
<rpc>
<edit-config>
<target>
<candidate/>
</target>
<default-operation>replace</default-operation>
<url>/var/tmp/$configFileName</url>
</edit-config>
</rpc>
Now i got the error message: syntax error, expecting <configuration> or <configuration-text>
Do you have any idea, how I can fix this?