Só mudar no XML, comigo funcionou perfeitamente.
<modification>
<id>snow 1.5.x</id>
<version>1.0.1</version>
<vqmver>1.0.3</vqmver>
<author>SuppliesProfessor</author>
<file name="catalog/view/theme/nome do tema/template/common/footer.tpl">
<operation>
<search position="before"><![CDATA[
</script>
]]></search>
<add><![CDATA[
<script language="javascript" src="catalog/view/javascript/snow.js"></script>
]]></add>
</operation>
</file>
</modification>