You could install the XML Tools plugin and use its XSLT Transformation feature.
Open Plugins Admin and install XML Tools plugin. After Notepad++ has been restarted paste the XSLT code from below to an empty tab and save it for example as ChangeVisible.xsl. Open the XML file you want to process. Go to (menu) Plugins -> XML Tools -> XSLT Transformation. In the dialog popping up click on the ellipsis button and in the file selector dialog popping up select the XSL file you created in step 2. In the options field of the dialog type UPCid='1234'. Click the Transform button. A new document will be opened with your changes applied. Save it to the original file.To change the value of the IsVisible node of more than one Item nodes, repeat steps 6 to 8.
The XSLT code. Please note: In line 19 (<xsl:template match="/RootNode/Item/IsVisible">) you have to provide the complete path to the IsVisible XML node, starting from the document’s root node.
<?xml version="1.0" encoding="UTF-8"?> <xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="xml" omit-xml-declaration="no" indent="yes" /> <xsl:param name="UPCid"/> <xsl:template match="@*|node()"> <xsl:copy> <xsl:apply-templates select="@*|node()"/> </xsl:copy> </xsl:template> <xsl:template match="/RootNode/Item/IsVisible"> <xsl:choose> <xsl:when test="../@UPC=$UPCid"> <xsl:copy> <xsl:copy-of select="@*"/> <xsl:text>False</xsl:text> </xsl:copy> </xsl:when> <xsl:otherwise> <xsl:copy> <xsl:copy-of select="@*|node()"/> </xsl:copy> </xsl:otherwise> </xsl:choose> </xsl:template> </xsl:transform>