These are the house rules and clarifications I used in my (now finished) Deathwatch campaign. These rules were in addition to the v1.0 errata (e.g. righteous fury at a sane level). If Rites of Battle looks sparse, I didn't felt the need to change much of what my players and I used from it in the campaign. Also, the campaign did not go on long enough to force a decision on whether the effects of plasma and melta weapons should be improved to make them more useful situationally than bolt weapons. I've bolded the page number of changes I feel made a significant difference to the campaign. If anyone wants to use these or comment, feel free.
Deathwatch Core Rulebook
p25: Generating Characteristics
After rolling nine times and recording the results, decide whether to reroll one.
Then match the final nine results as desired to the characteristics as desired.
p27: Deathwatch Astartes characters begin with 1,500xp to spend instead of 1,000xp. [this is to match the Sister of Battle/Crusader ascended character's starting xp]
p36: Omophagea. There is a very slight (and unspecified to players) chance of determinental feedback that rises if a large number of xenos brains are eaten in a short space of time. This will be represented by a willpower test (usually challenging +0)
p102: Astartes characters can treat the Medicae skill as an untrained basic skill for the purposes of first aid on Astartes characters and in the most basic use of the Narthecium and Reductor. [this is to allow kill-teams without an apothecary to perform minimal first aid and retrieve geneseed]
p105: Simply having a Tactics skill should give a space marine additional information about a relevant situation. The GM may call for a Tactics skill roll or a player may request it. If one is successful, the GM may make subsequent tests easier (e.g. reduce difficulty of silent move tests after a successful Tactics (Recon and Stealth) roll) or give additional relevant information.
p106: The Tracking skill is based on Perception not Intelligence.
p113: The Astartes Weapons Training talent includes use of the Astartes Sniper Rifle.
p114: Astartes characters do not automatically begin with the Chem Geld talent. [this to to dispel any such assumption]
p119: The talent Hatred (Tau) applies to Tau Empire battle formations, including their client races the Kroot and Vespids.
p134: The Shadow in The Warp (Tyranid) trait may have a greater area of effect in Tyranid occupied areas and worlds.
p156: The Arm Weapon Mounting may include pistol class flamer weapons such as the hand flamer.
p176: Under normal circumstances, bionic replacements will only be given to Astartes characters in the event of limb or organ loss. They cannot be requisitioned and the costs are for reference only. The only normal exceptions to this are the stated rules for Tech-marines and unspecified rules for Iron Hands and other augmentation-obsessed chapters.
p205: Burning fate points. An Astartes character has the second option available to Dark Heresy Ascended characters for burning fate points.
p208: All characters are restricted to a single basic or heavy weapon and one or two side-arms/melee weapons. Especially large melee weapons (e.g. two-handed weapons) may count as a basic weapon for these purposes. A sole basic weapon can be stowed to free the arms but a character with a heavy weapons must either drop it as a free action or spend a half action to switch the weight safely to one arm to free up the other arm.
For pistol and basic weapons, the default spare ammunition is three clips each (including special issue ammunition). Heavy weapons may have two spare clips in additional to an Astartes backpack ammo supply.
p228: The effects of Oaths can apply to non-Astartes killteam members at GM discretion. [generally this involves said character having an innate genius for combat tactics and/or prior experience fighting with Astartes, typically Dark Heresy Ascended level combat specialists]
p229: The +10 bonus to Willpower tests benefit of Oath to the Emperor applies to psychic power focus tests.
p245: A character with the Unarmed Warrior or Unarmed Master talents may choose to ignore the effects of one or both of these talents, thus reducing their unarmed damage accordingly. [useful if an Astartes wants to punch someone without causing too much harm and not use stun]
p246: An Astartes basic weapon may be fired one-handed but not with multiple attacks. The weapon may be held in one hand while another weapon is fired however. [I find the idea of effectively carrying multiple Astartes basic weapons outside of relic gear and combi-weapons ridiculous, let alone firing all of those]
p249: Weapons jams may be cleared by a successful BS or Tech-Use test, players choice. [the Tech-marine should be very effective at unjamming a weapon]
p360: The melee attacks of a horde may be dodged or parried by a character and the ranged attacks of a horde may be dodged. All dodge and parry tests are at a penalty equal to the attacking horde's current magnitude, unless the character has the Combat Master talent in which case the penalty is halved.
Horde attacks can be blocked by fields, treating each horde attack as a single attack for the purposes of blocking and burnout.
Deathwatch Rites of Battle
p59: Angels of Vengeance count as Dark Angels for all intents and purposes ruleswise.
p106: The Deathwatch Chaplain advanced specialty is only open to characters who have pursued the speciality for some time in game. Learning about the Primarchs etc. This *can* be represented by a break in-game of intense training but simply hopping into the rank with no preparation is not allowed.
Dark Heresy: Ascension
p48: A Sister of Battle with the Nascent Psyker trait may take the Mind's Eye Opens transition package. Additional psy rating and psyker talents can be obtained as elite advances.