dont change the spry validation, you should change the client validation to aloow for your date format.
change:
<input class="dateRange" name="S_UserRegistrationDate" type="text" id="S_UserRegistrationDate" onblur="if (document.getElementById('S_UserRegistrationDateServerValidation')) document.getElementById('S_UserRegistrationDateServerValidation').style.display='none';WAValidateDT(document.forms[0].S_UserRegistrationDate,'- Invalid date or time',true,/.*/,'yyyy-mm-dd','','',false,/.*/,'','','',document.forms[0].S_UserRegistrationDate,0,true)" value="<?php echo((isset($_GET["S_UserRegistrationDate"]))?$_GET["S_UserRegistrationDate"]:"") ?>" size="15" />
</span> to <span id="sprytextfield3">
<input class="dateRange" type="text" name="S_UserRegistrationDate2" id="S_UserRegistrationDate2" value="<?php echo((isset($_GET["S_UserRegistrationDate2"]))?$_GET["S_UserRegistrationDate2"]:"") ?>" onblur="if (document.getElementById('S_UserRegistrationDateServerValidation')) document.getElementById('S_UserRegistrationDateServerValidation').style.display='none';WAValidateDT(document.forms[0].S_UserRegistrationDate2,'- Invalid date or time',true,/.*/,'yyyy-mm-dd','','',false,/.*/,'','','',document.forms[0].S_UserRegistrationDate2,0,true)" size="15" />
to:
<input class="dateRange" name="S_UserRegistrationDate" type="text" id="S_UserRegistrationDate" onblur="if (document.getElementById('S_UserRegistrationDateServerValidation')) document.getElementById('S_UserRegistrationDateServerValidation').style.display='none';WAValidateDT(document.forms[0].S_UserRegistrationDate,'- Invalid date or time',true,/\b([12]\d|3[0-1]|0?[1-9])\/(1[0-2]|0?[1-9])\/\d{4}\b/,'yyyy-mm-dd','','',false,/.*/,'','','',document.forms[0].S_UserRegistrationDate,0,true)" value="<?php echo((isset($_GET["S_UserRegistrationDate"]))?$_GET["S_UserRegistrationDate"]:"") ?>" size="15" />
</span> to <span id="sprytextfield3">
<input class="dateRange" type="text" name="S_UserRegistrationDate2" id="S_UserRegistrationDate2" value="<?php echo((isset($_GET["S_UserRegistrationDate2"]))?$_GET["S_UserRegistrationDate2"]:"") ?>" onblur="if (document.getElementById('S_UserRegistrationDateServerValidation')) document.getElementById('S_UserRegistrationDateServerValidation').style.display='none';WAValidateDT(document.forms[0].S_UserRegistrationDate2,'- Invalid date or time',true,/\b([12]\d|3[0-1]|0?[1-9])\/(1[0-2]|0?[1-9])\/\d{4}\b/,'yyyy-mm-dd','','',false,/.*/,'','','',document.forms[0].S_UserRegistrationDate2,0,true)" size="15" />