There is an odd codex (or supplement) page floating around, that has the Thousand Sons entry on it. The primary odd thing about the page, is that the number on it is 19. That just does not fit the Chaos Space Marine codex.
The page itself looks exactly like a codex page, in just about every way, and if it is a fake, its a damn good one.
While right now I am still in Edmonton Alberta on vacation, its hard for me to check the entry for stat line changes, but there is quite a bit that looks different from what I recall. Since my memory though on specific codex entries, I am going to just do a quick run down of what is on the page and those with the codex available can check for any differences.
Please remember that this is not confirmed as real. It is an odd rumor floating out there.
Thousand Son
Standard Stat lines that I am sure are not different
Special Rules
Fearless, Mark of Tzeentch, Psyker (mastery level 1, aspiring sorceror only), The Sorceror Commands, Veterans of the Long War, Feel No Pain, (thousand sons only)
Psyker
The sorceror knows the Pink Fire Psychic Power from the Lore of Tzeentch
The Aspiring Sorceror may take a single primaris power from Telekinesis, Telepathy, Biomancy, or divination
The Aspiring Sorceror may take a single psychic power from teh discipline of Tzeentch or any other discipline for which he knows the primaris power
One model can take an icon of flame