How to write new rules from code behined in web.config

How to write new rules from code behined in web.config

I have applied URL rewrite in my application and define some rules in
web.config as
<modulesSection>
<rewriteModule>
<rewriteOn>true</rewriteOn>
<rewriteRules>
<rule source="About/About-test"
destination="About/About.aspx"/>
<rule source="test-In-Media"
destination="Others/MediaUpdates.aspx"/>
<rule source="Home" destination="MasterPage/HomePage.aspx"/>
</rewriteRules>
</rewriteModule>
</modulesSection>
<httpModules>
<add name="RewriteModule" type="RewriteModule.RewriteModule,
RewriteModule"/>
<add name="ScriptModule"
type="System.Web.Handlers.ScriptModule, System.Web.Extensions,
Version=3.5.0.0, Culture=neutral,
PublicKeyToken=31BF3856AD364E35"/>
</httpModules>
Now i want to add some new rules programmatically. How can I achieve this??