이럴 경우 최근 게시글 위젯 자체를 다시 만드셔야 합니다.
widgets/newest_document/queries/getNewestDocument.xml 파일을 보시면요

<query id="getNewestDocuments" action="select">
    <tables>
        <table name="documents" />
    </tables>
    <columns>
        <column name="*" />
    </columns>
    <conditions>
        <condition operation="in" column="module_srl" var="module_srl" filter="number" />
        <condition operation="equal" column="category_srl" var="category_srl" pipe="and" />
    </conditions>
    <navigation>
        <index var="sort_index" default="list_order" order="order_type" />
        <list_count var="list_count" default="20" />
    </navigation>
</query>

라고 되어 있는데

<query id="getNewestDocuments" action="select">
    <tables>
        <table name="documents" />
    </tables>
    <columns>
        <column name="*" />
    </columns>
    <conditions>
        <condition operation="in" column="module_srl" var="module_srl" filter="number" />
        <condition operation="equal" column="category_srl" var="category_srl" pipe="and" />
        <condition operation="equal" column="extra_vars번호"  default="원하는 값" pipe="and" />

    </conditions>
    <navigation>
        <index var="sort_index" default="list_order" order="order_type" />
        <list_count var="list_count" default="20" />
    </navigation>
</query>

위와 같이 <condition operation="equal" column="extra_vars번호"  default="원하는 값" pipe="and" /> 를 추가해주시면 됩니다.

로 바꾸시면 될듯합니다.