Web Forms :: How To Edit 'siteMapFile' Attribute Of SiteMap Provider In Web.config Dynamically

I want to add/edit available siteMap providers in web.config file from code behind.

I am using the siteMap providers currently in the application web.config in a format given below:

<siteMap>
<providers>
<add siteMapFile="~/App_Themes/MyAppDefault/MySiteMap.sitemap"
name="MyAppDefault" type="System.Web.XmlSiteMapProvider" />
</providers>
</siteMap>

This is allowing my application user to show up a different Site Map as and when the theme is changed.

But when I tried to do the same with the following code I faced with an issue.

configuration = WebConfigurationManager.OpenWebConfiguration("~")
section = CType(configuration.GetSection("system.web/siteMap"), SiteMapSection)
Dim provider As New ProviderSettings()
If Not section Is Nothing Then
provider.Name = txtError.Text
provider.Type = "System.Web.XmlSiteMapProvider"
section.Providers.Add(provider)
configuration.Save()
End If

This code is not allowing a provider.siteMapFile property (provideer is the ProviderSettings object).
As well the maximum possible way I can add a new SiteMap provider in web.config is as follows

<siteMap>
<providers>
<add name="MyAppCustom" type="System.Web.XmlSiteMapProvider" />
</providers>
</siteMap>

If anybody can suggest a way for me to add/edit the 'siteMapFile' attribute of the provider.