In the beginning, I use CSS with no-steam, so somehow certain steam id is given. Later, I use steam-based CSS, so I was given a new steam ID. With same nickname, my statistic produce 2 names (same name). How can I combine those two into single name ?

I don't think that this is possible...

[Call me when humans go extinct]

gameMe stats resets every three months, there are only 7 days before the next reset. So there will be no need to transfer your status.