Armor Mods offer a wide berth of possible additions to any number of armor systems, from basic material upgrades to complex subsystem inclusions. They can enhance protection of the armor directly, increasing the amount of damage it absorbs, or they can offer additional utility to the armor wearer. Below are some additional armor mods which can be added to an appropriate armor.
Heat Sinks: Similar to Refractive Glazing (p. 313 EP) this modification embeds heat conducting elements into the surface of the armor, but instead of trying to radiate it immediately it stores it in heat sink systems built into the armor. This means that it can reduce much more heat than the Glazing, but it only does so until the sinks reach a high enough temperature at which point heat is no longer easily conducted to them - so they must be cooled or vented. This mod will absorb 20 points of Energy damage related to heat - after which it's heat sinks must vent for a full Action Turn in order to be used again. This mod does not dump heat properly in vacuum, and may become damaged over repeated uses and need to be replaced or repaired over time. These units are much more effective on vehicles or large bots than people. [Moderate]
Mag-Lock System: Once a vital component to many vacuum suits and vac-rated armors, Mag-Locks have become less common in face of grip materials and other advanced technologies, but can still be fairly common in some armors. Primarily located in the hands and feet, these systems can also involve electromagnetic studs which can hold tools or other objects on the surface of the armor. Primarily, it grants benefits similar to the Magnetic System (p 311 EP) allowing them to grip or walk on magnetic surfaces even in zero-g, though for most this will be at reduced speed, and grants a +20 to hold on to magnetic surfaces or objects if a test is required. Can only be equipped on armor which could cover the hands and feet. [Low]
Microthrusters: This mod embeds small thrust modules with fuel in the armor's exterior, which are controlled with gestures or remote commands. It can only be equipped on body-covering armor and vacsuits, or Exoskeletons. In an exoskeleton, it adds Vector Thrust (8/40) as a mobility system, but for conventional armor it does not tend to normally "fly" as such, but gives a +10 to Free Fall tests as it aids in maneuverability in those situations. It has enough fuel for about an hour of minimal controlled bursts, or 10 minutes of continuous burn. In low gravity, microthrusters can be used to catch oneself from a fall, "glide" over the ground or boost normal jumps to greater heights - though outright flying will quickly use up the fuel. [Moderate]
Reinforced Knuckles: The "brawler" of armor upgrades, this mod includes heavier reinforcement on joints used for strikes, as well as additional studs, spikes or plates such as on the hands and feet. This makes unarmed blows using the armor more potent and harmful to an enemy, if you know what you're doing, and such enhancements are already included on some armors, like the Crasher Suit. This mod adds 1d10 DV when making Unarmed Attacks in the armor, and can only be equipped to armors which could cover the hands and feet. [Low]
(Also, shout out to a kind Anon, who collected all of H-Rep in downloadable form, in pdf and docx, with TOC and everything, which is available here. They said they'll keep it updated.)