stackoverflowさん、そのままです
app.configのconfigSectionsセクションに追加セクション（MajorCommands）を記載
[code]
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="MajorCommands" type="System.Configuration.DictionarySectionHandler" />
</configSections>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
</startup>
<appSettings>
省略･･･
</appSettings>
<MajorCommands>
<add key="Standby" value="STBY"/>
<add key="Operate" value="OPER"/>
<add key="Remote" value="REMOTE"/>
<add key="Local" value="LOCAL"/>
<add key="Reset" value="*RST" />
</MajorCommands>
</configuration>
[/code]

C#ではConfigurationManagerのGetSectionでセクション以下をハッシュに読み込み
[code]
System.Collections.Hashtable nb = System.Configuration.ConfigurationManager.GetSection("MajorCommands") as System.Collections.Hashtable;
[/code]