Hätte dies vorgeschlagen:
<xsl:template match="LineText" />
<xsl:template match="Item[not(ItemDeliveryInformation)]">
<xsl:copy>
<xsl:apply-templates select="node() | @*" />
<ItemDeliveryInformation>
<LineNumDeliveryNote>0</LineNumDeliveryNote>
<PackingSlipId>
<xsl:value-of select="/SALESINVOICE/HeaderInformation/InvoiceNumber"/>
</PackingSlipId>
<DeliveryDate>
<xsl:value-of select="/SALESINVOICE/HeaderInformation/InvoiceDate"/>
</DeliveryDate>
<DeliveredQuantity>
<xsl:value-of select="TotalQuantity"/>
</DeliveredQuantity>
</ItemDeliveryInformation>
<xsl:copy-of select="LineText"/>
</xsl:copy>
</xsl:template>