It was probably foolish to transfer the rules of the setting from my actual rules document into these pages, because if I made updates to the rules document, they obviously don't cascade. For the best and most up to date rules, I actually recommend that you ignore the SYSTEM part of this site and just go get the pdf of the most up to date rules. I'll leave them here as an archive regardless.
https://drive.google.com/file/d/1i6SlE8bF1mmGmgMKtkj2OHoP_-FrtKAo/view?usp=sharing
In addition to those rules, the following Eberron specific rules need to be addressed:
Eberron Races
Warforged: +4 to resisting poison, disease, sleep, and anything else that wouldn't normally affect a construct. (Normally constructs are immune to all these things, but a +4 is enough of a bonus to shield them against any level-appropriate attack.)
Shifters: Just use the woodwose rules from the document above. They are conceptually the same thing anyway.
Changelings: Change form as move action, +1 to Subterfuge, +1 to Communication
Kalashtar: Can spend 1HP to establish a two-way mindlink with a creature it can see, +1 to Communication, +1 to Knowledge
Dragonmarks
Dragonmarks are a special application of magic that occurs outside the system, so to speak. Dragonmarked magic is more subtle than regular magic, and is more focused on creating things or providing a very specific service. It is quite likely that the source of this magic is different than that of sorcery. However, given the way that my system's Lovecraftian magic differs from standard Vancian magic, I've decided that there needs to be an impact on this on Dragonmarked characters as well.
First of all, Dragonmarked characters are the only subsystem in this game that is not self-contained, i.e., you will need to refer to your 3.5 edition Eberron Campaign setting book to use them. I don't actually envision that being a Dragonmarked character is really something that player characters do, but if for some reason you need mechanics for it, just use those from the 3.5 book. Yes, it refers to spells that are also in the 3.5 edition books rather than here, but use them as they would be in 3.5. However, least dragonmarked effects have the same sanity impact required as if casting a 1st level spell. Lesser dragonmarked effects are as if casting a 2nd level spell, and greater dragonmarked effects are the equivalent of a 3rd level spell. The spell levels are relatively low, because the dragonmarks protect the user somewhat from the sanity damage that is required if you are doing it without one (i.e., the effects should normally be equivalent to 1st, 3rd and 5th respectively). However, there is still a risk involved, which is why the use of dragonmarks is highly regulated by the Houses, in order to protect them from the wrath of the populace and the governments of the various kingdoms both, as well as the impacts of their dragonmarked heirs going insane.
I would also assume the optional Lovecraftian slide of Sanity on a natural 1 applies to Dragonmarked usage as well; i.e., a failure of a natural 1 on any roll pertaining to using your Dragonmark causes a permanent -1 to your Sanity score. Because of this, the career of a dragonmarked heir is often rather short and bright, and over time, they must either be put down or locked away by the house as they slide further and further into madness because of the use of their marks. However, the risk of the hounds of Tindalos coming for you if you fail on a natural 1 does not apply to Dragonmarks. This is a big part of why Dragonmarked magic is more socially acceptable to those who are in the know; it provides a service to society, and the only person at risk is the Dragonmarked himself.
Personally, I don't envision that many (if any) players will have any interest in having Dragonmarks themselves, but if they do, they must give up one of the minor class abilities of their class in order to take it, referring to the class customization options in the character generation section of the rules. You start out at 1st level with the least Dragonmark of the type you have chosen, and at 4th level it advances to lesser status, growing to greater status at 7th level.