I was holding back with the idea for these while we were all waiting for Rites of Battle, to see if anything similar was poised to exist. Turns out... there wasn't anything quite like these in there, so I was free to dabble, and I put together the first, rough draft of these additional Special Abilities for Apothecaries, Assault Marines, Devastators and Tactical Marines.
Some of them are written for specific chapters, allowing players to build their Assault Marine as a Blood Claw, or their Apothecary as a Sanguinary Priest. Others are simply there to offer more options beyond those in the rulebook.
These abilities are designed to be options alongside those abilities in the rulebook, free to be selected by any eligable character in place of the likes of Unrelenting Devastation, Bolter Mastery, etc.
Apothecary
Sanguinary Priest (Blood Angels only)
The Apothecaries of the Blood Angels differ from those of other Chapters in several ways. Owing to the nature of the Blood Angels' curse, the Chapter's Apothecaries are as vital to the spiritual guidance of their brethren as the Chapter's Chaplains, exhorting control over the dark fury that consumes the Sons of Sanguinius. These Sanguinary Priests must practice what they preach, for the necessary bloodletting of the Apothecary's calling, whether to heal their brothers or to claim their geneseed evokes the Red Thirst's terrible grip upon their minds, turning their most crucial of duties into a spiritual trial that must be overcome time and again. To aid them, to bolster their resolve against the darkest parts of themselves, each narthecium in use by the Sanguinary Priests contains a blessed fragment of one of the Blood Chalices, each imbued with the merest fragment of Sanguinius' grace, urging the priests and their nearby brethren to greater glories.
A Blood Angels Apothecary gains a +3 bonus to all Willpower Tests and may enter a Frenzy (if he has that Talent) as a Free Action. The same benefit is conferred to any Blood Angels in Squad Mode with the Apothecary.
Assault Marine
Master of Blades
The Assault Marine gains a +10 bonus to all Weapon Skill Tests and +2 to Damage when wielding a bladed melee weapon (combat blade, sword, chainsword, etc). This ability only functions in Solo Mode.
Scornful Defence
The Assault Marine knows well when to go for the kill and when to throw his foes aside dismissively for his brothers to slay. When the Assault Marine parries or dodges an attack, his squad-mates gain +10 to hit against the attacking enemy. This ability only functions in Squad Mode.
Reckless Charge (Space Wolves only)
Still hot-blooded and vital with the youthful fury of a young pup, the Battle Brother throws caution to the wind when he charges, lashing out with deadly abandon. When performing a Charge Attack action, the Battle Brother may spend his Reaction to make an additional attack with the same bonuses to hit. This ability may only be used in Solo Mode.
Wrathful Crusader (Black Templars only)
The righteous hate of the Black Templars is strong, and many of their Assault Marines learn to turn that loathing into lethality. When making a melee attack against an enemy he Hates, the Assault Marine deals an additional +2 damage to individual enemies, or +1d5 points of Magnitude damage against a Horde. This ability may only be used in Solo Mode.
Devastator
Covering Fire
The Devastator's timing is perfect, every shot flawlessly delivered to grant his brethren moments of respite from the deadly attentions of the enemy, fleeting moments enough to act. In any turn where the Devastator hits with a Heavy weapon by 4 or more Degrees of Success, he may grant a single Battle-Brother within Support Range a bonus Half Action, during his next turn which may not be used for any attack action, focus power action or any action with the Concentration sub-type. This ability may only be used in Squad Mode.
Inescapable Wrath
If the Devastator spends at least a Half Action aiming before an attack with a Heavy Weapon, all attempts to dodge that attack suffer an additional -10 penalty. This ability may only be used in Solo Mode.
Wisdom of Ages (Space Wolves only)
The Marine is long of tooth and long-practiced at delivering firepower where it is needed most. When the Devastator makes an Aim action, he may attempt a Challenging (+0) Awareness Test; if successful, his subsequent attack gains +1 Pen, with an additional +1 for every two Degrees of Success. This Awareness Test gains a +10 bonus if he aims as a Full Action. This ability may only be used in Solo Mode.
Restraining the Curse (Blood Angels only)
Those Sons of Sanguinius who serve as Devastators must constantly fight to restrain their darker urges so that they can fulfill their battlefield role. The Devastator may re-roll all tests to resist succumbing to the Black Rage.
Tactical Marine
Mentor
The Marine's skill at guiding and aiding others makes him a boon to his squad, his experience helping them achieve even greater victories. Any character the Battle-Brother assists gains an additional +10 bonus to their test, and all Battle-Brothers in his squad may treat any skill he is Trained in as a Basic Skill. This ability may only be used in Squad Mode.
Tactical Flexibility
The Tactical Marine is proficient in every method and tool of war in use by the Astartes. The Battle-Brother treats all Drive, Pilot and Tactics skills as Basic skills, and only suffers a -10 penalty for using a weapon untrained. Any Drive, Pilot and Tactics skills he is Trained in gain a +5 bonus.
Patient Hunter (Space Wolves only)
The Marine is cunning and careful, moving to capitalise upon the briefest moments of weakness. The Marine may, as a free action, take a single half action (which may not be an attack or any action with the concentration subtype) when he causes an enemy to be stunned, pinned or Critically Injured. This ability may only be used in Solo Mode.
Stern Crusader (Black Templars only)
The Templar's wrath knows no limitations, and his fury is as easily expressed with a storm of fire as with the clash of blades. The character gains the benefits of the Hatred talent with ranged attacks as well as with melee attacks. This ability may only be used in Solo Mode.
As I said, this is the first draft, rough and basic. I'm open to suggestions for improvements or additional abilities (particularly ones for other Chapters), so feel free to comment.