您可以使用SqlConnectionStringBuilder Class获取和编辑连接字符串。
这里的连接字符串是方法的本地，但在下面方法范围内的任何地方。

public static void ChangeConnectionStringFromExisting()
{

    var connectionString = "Server=localhost;Integrated security=SSPI;database=master";

    var builder = new SqlConnectionStringBuilder(connectionString);

    builder.DataSource = "(LocalDB)\\MSSQLLocalDB";
    builder.InitialCatalog = "MyAppDatabase.mdf";

    connectionString = builder.ConnectionString;

    using (var cn = new SqlConnection(connectionString))
    {
        // . . .
    }

}