I noticed in "Dark Heresy - Daemon Hunter" on 101 page, there is "Sorcery of Tzeentch".

sorcery of TZeeNTch
The Sorcery of Tzeentch is a collection of Minor Psychic Powers unique to daemons of Tzeentch. Psykers wishing to learn these powers must treat the Sorcery of Tzeentch as its own (albeit small) Psychic Discipline. These powers count as both Psychic Powers and Sorcery for any effects relating to either.
Fire of Tzeentch is an eldritch, multi-hued Warp energy that is a signature of Tzeentch and his minions. Any ability that summons fire or causes Energy damage used by a servant of Tzeentch creates Fire of Tzeentch instead of mundane flame. While its effects are similar, its appearance is incredibly disturbing.
warP fire
Threshold: 9
Focus Time: Half Action
Sustained: No
Range: 30m
The Daemon summons a torrent of magical energy that burns with Chaos. It may manifest Warp Fire anywhere within range and line of sight. This power deals 1d10+Psy Rating Energy Damage.
Overbleed: For every 9 points by which the Daemon exceeds the Threshold, increase the damage by 1d10.
BooN of muTaTioN
Threshold: 18
Focus Time: Full Action
Sustained: No
Range: 5m
The power of the Daemon is enough to cause its victim’s body to warp and twist itself apart. The target suffers 1d10 Toughness Damage. If the target is slain it becomes a Lesser Chaos Spawn (see page. 98) under the control of it's new daemonic master.
Overbleed: For every 9 points by which the Daemon exceeds the Threshold, increase the damage by 1d10.
BoLT of TZeeNTch
Threshold: 27
Focus Time: Full Action
Sustained: No
Range: 45m
This powerful blast of Warp energy manifests as a solid beam of force and swirling light. Anything in its path is burnt in a furnace of pure Warp fire, melting stone and metal, or vaporizing anything else. The target suffers 1d10 per Psy Rating Energy damage. This damage is treated as Unstable (see page 130 of the DARK HERESY Rulebook) and has a Penetration of 4+Psy Rating. Overbleed: For every 9 points by which the Daemon exceeds the Threshold increase the damage by 1d10. If the daemon exceeds the Threshold by 18, the damage gains the Tearing Quality

Is says that these powers are both Psychic Powers and Sorcery for any effects relating to either.

1) Does this mean, that even a sanctioned psyker can learn it and use them as normal Psychic Powers from any other discipline and does not get any corruption from using it?.

2) If you are sorcerer, you can choose these powers, but you get corruption from using it because sorcerer rules apply?

To learn these powers I imagine, you need to buy discipline with psy rating and maybe some other prerequisites. What do you think what it should be?

anyone?

Personally, from what I can see, I'd allow a Psyker to learn them as normal Psychic Powers /but/ they would have to choose "Sorcery of Tzeench" as a specific Psychic Discipline first, and I, as the GM, would probably force my players to have Forbidden Lore: Daemonology to even know about these powers (and after that, engage in lengthy studying of these abilities). And finally, they'd probably gain Corruption instantly, for dabbling in the heretical arts.

So, I gues that the order of prerequisites would be :

1) get forbidden Lore: Daemonology

2) ask GM to include some plot hooks and try to find some scrolls

3) choose "Sorcery of Tzeench" as Psychic Discipline (and of course this brings corruption)

4) to learn additional powers, find more scrolls (and of course this brings corruption for each learnt power)

but one question remains: does successfull manifestation brings corruption like arcana powers?
"

Dark Power

I would leave the present drawbacks intact. Would encourage getting Dark Soul to mitigate it further.

Of course if you're playing them as Psychic Powers you could get really creative as a GM if you want to. There's plenty of possibilities. Instead of Psychic Phenomena, 9's are automatically Perils of the Warp for example (off the top of my head).

yes, my PC is a psyker and it seems I could use these powers as psychic Powers without this "Dark Power" which affects Arcana.

Also, my PC has a Dark pact with Tzeench and he doesnt know it. However, he noticed strange things happening around.
this PC is named "Chaos" and was taken from capsule which was found in asteroid hulks. He does not remember anything. He has a huge hatred on universe somehow and wants to destroy universe whatewer the cost. On the brink of the death, he got even angrier and asked for help (earlier he and another acolyte got some crasy encounter with a deamon traveling through the warp, because they tried to talk to it and blather it till we landend on the planet.)

So the dark pact binded my las pistol with some strange energy. got some corruption. when it rolls to hit, on odd number, psychic phenomena happens on the target. Also, on every playing a PC must sacrifice 1 good or two bad people, or roll WP to prevent corruption. Also, if somebody tries to take this weapon, phenomena happens. Also, if PC would trie to leave it, very hard roll and even perils can happen. Since then we got unbound deamon, blood raining, warp swallowing and other things happening around. Nobody had a clue. A month ago, PC witnesed deamon binding into same las pistol. So now, this weapon is deamon weapon. So, I gues this dark pact could bring "Sorcery of Tzeench" also.