How to access the Web.Config and ProjectProperties at Design Time

DesignTimeConfig config = new DesignTimeConfig(this.Site);

Then use config.WebConfig to manipulate the XmlDocument...

using System;
using System.ComponentModel;
using System.ComponentModel.Design;

using System.Globalization;

using System.Resources;
using System.Xml;

using EnvDTE;

namespace UITemplates
{ 
 public class DesignTimeConfig
 {
  private XmlDocument _webConfig;
  private EnvDTE.ProjectItem _projectItem;
  private IServiceProvider _serviceProvider;

  public DesignTimeConfig(IServiceProvider serviceProvider)
  {
   _serviceProvider = serviceProvider;
  }
  public object GetService(Type type)
  {
   return _serviceProvider.GetService(type);
  }
  public XmlDocument WebConfig
  {
   get
   {
    string projectPath;
    string filename;
    if(_webConfig!=null)
     
    {
     return _webConfig;
    }

    XmlDocument configXml = new XmlDocument();
    projectPath = ProjectProperties.Item("ActiveFileSharePath").Value.ToString();
    filename = projectPath+ @"\web.config";
    configXml.Load(filename );
    _webConfig = configXml;
    return configXml;
   }
  
  }
  internal EnvDTE.Properties ProjectProperties
  {
   get
   {
    return ProjectItem.ContainingProject.Properties;
   }
  }
  internal EnvDTE.ProjectItem  ProjectItem
  {
   get
   {
    if(_projectItem==null)
    {
     _projectItem =(EnvDTE.ProjectItem)GetService(typeof(EnvDTE.ProjectItem));;    
    }
    return _projectItem;
   }
  }
  /// <summary>
  /// Gets the value from an <appSettings><add /> element
  /// </summary>
  /// <param name="key"></param>
  /// <returns></returns>
  public string AppSettings(string key)
  {
   XmlNode designLangNode = WebConfig.SelectSingleNode("//appSettings/add[@key='" + key + "']");
   if(designLangNode==null)
   {
    return String.Empty;
   }
   XmlAttribute currentValue = designLangNode.Attributes["value"];
   if(currentValue==null)
   {
    return String.Empty;
   }
   return currentValue.Value;
  }

public string GetProjectProperty(string name)
  {
   
   return ProjectProperties.Item(name).Value.ToString();
   
  }

 }
}

There is a posting here about it here, but as I commented, I prefer Site.GetService :
http://blogs.msdn.com/mszcool/archive/2004/06/30/169793.aspx

To get the project properties, you can call GetProjectProperty with the names from here : http://msdn.microsoft.com/library/en-us/vbcon/html/vbconthemacroprojectobjectmodel.asp?frame=true