How to implement the logout from VK.COM in the standalone app

I'm developing the application for Windows Phone and Windows RT which is a social network VK.COM client. For a long time I have been searching for a way to implement logout from it. It was not trivial task because VK API is not supporting logout. 

While I was searching the solution in the internet I saw two kinds of the solution: 

1. So-called "direct authorisation" which allows to authorizate in the application with the login and the password. It is avaible only for applications which are aprooved by vk and it requires an "eternal" token. But some developpers disassemble foreign applications and steal eternal tokens.
2. Deleting the cookies with authorization data.

I have choosed the second one. There is code below which deletes necessary cookies and must be called before logging in of the other user.

Code:

var myFilter = new Windows.Web.Http.FiltersHttpBaseProtocolFilter();
var cookieManager = myFilter.CookieManager;
var myCookieJar = cookieManager.GetCookies(new Uri("https://oauth.vk.com"));
foreach (var cookie in myCookieJar)
{
   cookieManager.DeleteCookie(cookie);
}

Renaming of an application in the windows phone store

Hello.
I have one issue with the windows phone store that has not resolved. I had a long correspondence with the develpment support, but they didn't get a help. The essence of the issue - renaming of an existing app for WP 8.1 in the windows phone store. There is instructions in MSDN about this process where is written that I can just create new submission and enter new name. But no ! I can't ! The hame field is disabled ! I asked on Stackoverflow, on MSD forum, but nobody has responded me.
So, I've creted new application with desired name and hided old application from the store.
If you know how to resolve that problem -  please tell ! I'll be very glad !