Have you tried Launch.CMD? I think the following is working in the way you describe -- moving a file and overwriting a file of the same name if it exists at the destination path. (I haven't rigorously tested this -- just once with a text file.)
<?xml version="1.0" encoding="utf-16"?>
<!--VoxCommando 2.2.3.5-->
<command id="69" name="move and overwrite file" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>Launch.CMD</cmdType>
<params>
<param>MOVE /Y "yourfile_sourcepath" "yourfile_destinationpath"</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<phrase>move and overwrite file</phrase>
</command>