The Steam_api.dll's edit is totally working, but really easy to patch so this Thread should delete (well despite that AlterIW staffs must already know this exploit), I have played without changing my XUID and the Steam_api.dll's edit work (made with WinHex).
Well... No matters whats they(the AlterIW staffs) did, the ban now looks really un-bypassable by now, the Steam_api.dll's edit dont work anymore (but they didnt update it) and last evening It was.
And for the XUID/Mac adress changer, I succesfully changed my XUID 3 times (I saw the new XUID value in the console) and I can say you that I got all the three times the "u're ban" message (sometime not poping-up right after the game loaded).
So... I think they found a way out to really ban us permanently, I readed in the console about a SteamAuthId value showing up (looking exactly like this :"Steam auth server ID is 0x**************** ", where * are numbers) and I believe that maybe, they use now this value and I dont know if there is even a way to change it.