c# - Little utility to add element in .config app file -

i need make little utility upgrade xml .config c# application file outside application.

i need add element:

<?xml version="1.0"?>   <configuration>    ...    ...    <startup uselegacyv2runtimeactivationpolicy="true">     <supportedruntime version="v4.0" sku=".netframework,version=v4.5.2"/>   </startup> </configuration> 

wich easy way?

i use xslt. example:

source

<?xml version="1.0"?> <configuration>     <somexml/> </configuration> 

transformation

<?xml version="1.0" encoding="utf-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/xsl/transform">     <xsl:output encoding="utf-8" indent="yes" method="xml"/>     <xsl:template match="@*|node()">         <xsl:copy>             <xsl:apply-templates select="@*|node()"/>         </xsl:copy>     </xsl:template>     <xsl:template match="configuration">         <xsl:copy>             <xsl:apply-templates select="@*|node()"/>             <startup uselegacyv2runtimeactivationpolicy="true">                 <supportedruntime version="v4.0" sku=".netframework,version=v4.5.2"/>             </startup>         </xsl:copy>     </xsl:template> </xsl:stylesheet> 

target

<?xml version="1.0" encoding="utf-8"?> <configuration>     <somexml/>     <startup uselegacyv2runtimeactivationpolicy="true">         <supportedruntime version="v4.0" sku=".netframework,version=v4.5.2"/>     </startup> </configuration>