Grey Knight Mastery Levels

[Delfin07]

So for the fact of all Grey Knights having the Hammer ability to use for combat, can you switch out that ability for something in the rule book? or are they stuck with the ability?

[Katharon]

So for the fact of all Grey Knights having the Hammer ability to use for combat, can you switch out that ability for something in the rule book? or are they stuck with the ability?

They only have the ability that is mentioned in their army list entry. You are not allowed to exchange it unless it clearly says so.

[DarkLink]

Since it's a pre-6th codex, you need to check the FAQ. The FAQ specifies that only Inquisitors and Librarians may exchange psychic powers, everyone else is stuck with what they've got. Otherwise, GKs would probably still be as powerful as they were back in 5th.

[Nabterayl]

No. Remember that most Grey Knights can't use rulebook disciplines at all - only librarians. But librarians can never exchange Hammerhand for a rulebook power. As the [url=http://www.games-workshop.com/MEDIA_CustomProductCatalog/m3440038a_Grey_Knights_v1.5_September_13.pdf]FAQ[/url] says:

A Grey Knights Librarian may use the psychic disciplines found in the Warhammer 40,000 rulebook, instead of those in Codex: Grey Knights. If he does so, generate a number of psychic powers equal to his Mastery Level from the Divination, Pyromancy or Telekinesis disciplines (in any combination) before armies are deployed. If he does so he may not purchase additional powers. Hammerhand cannot be exchanged in this manner, but is instead retained in addition to the powers purchased or generated by the Librarian.