Change connection string dynamically in ASP.NET C#

<connectionStrings>
  <add name="MyCon1" connectionString="server=.\SQL2008; database=DB1; Trusted_Connection=true;"/>
  <add name="MyCon2" connectionString="server=.\SQL2008; database=DB2; Trusted_Connection=true;"/>
  <add name="MyCon3" connectionString="server=.\SQL2008; database={0}; uid={1}; pwd={2};"/>
</connectionStrings>

SqlConnection con = null;

if (someCondition)
{
    // use MyCon1
    con = new SqlConnection(ConfigurationManager.ConnectionStrings["MyCon1"].ConnectionString);
}
else
{
    // use MyCon2
    con = new SqlConnection(ConfigurationManager.ConnectionStrings["MyCon2"].ConnectionString);
}
            
// or you can construct the string manually.  I'm going to assume you want to use
// data from your controls in the string, so if you have a variable for the database
string dbToUse = "mydb";
con = new SqlConnection(string.Format("server=.;database={0};", dbToUse));

// or you could put the tokens in the connection string itself and keep it in the web config
string username = "me";
string password = "mypassword";
            
con = new SqlConnection(string.Format(ConfigurationManager.ConnectionStrings["MyCon3"].ConnectionString, dbToUse, username, password));