How to append connectionString from one config file to other config file

[NarVish]

Hi, I'm trying to copy connectionStrings from C:\test2\web.config to c:\test1\app.config. In web.config, connectionString element looks as below. both config files are not belong to my project.

<connectionStrings>
<add name="SqlServerConnectionString" connectionString="server=NAPALDEVDBS02.dev.psisystems.local\DEV08; database=VPO1; User ID={0}; Password={1}; Pooling=True; Min Pool Size=5; Max Pool Size=40; Connect Timeout=10;" providerName="System.Data.SqlClient" />
<add name="SqlServerConnectionPropertiesString" connectionString="Initial Catalog=VPO1;Integrated Security=False;Uid=WSAccountData;Pwd=drUc5u8r;" providerName="System.Data.SqlClient" />
<add name="VPO1" connectionString="server=NAPALDEVDBS02.dev.psisystems.local\DEV08; database=VPO1; User ID=VPOServer; Password=Mon186ster;" />
</connectionStrings>

ExeConfigurationFileMap fileMap = new ExeConfigurationFileMap();

fileMap.ExeConfigFilename = @"c:\test1\app.config";
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(fileMap, ConfigurationUserLevel.None);

var connectionStringsSection = (ConnectionStringsSection)config.GetSection("connectionStrings");

ExeConfigurationFileMap fileMapWeb = new ExeConfigurationFileMap();
fileMapWeb.ExeConfigFilename = @"C:\test2\web.config";
Configuration configWeb = ConfigurationManager.OpenMappedExeConfiguration(fileMapWeb, ConfigurationUserLevel.None);

var connectionStringsWeb = (ConnectionStringsSection)configWeb.GetSection("connectionStrings");

//here I got connectionString element in connectionStringsWeb from web.config file. But how to append this connectionString element to app.config file.

Thanks in advance.