What Racial Mechanics, impact
Warforged Culture? I would say Constructed Resilience?
Yep! Not needing to sleep, eat, drink, or breathe would impact the culture a ton. For example, they would be perfect ambassadors between aquatic races (like Merfolk) and land-dwelling races, because they don't need to breathe and can just walk around on the ocean floor to travel to the homes of the aquatic races. They also would be great at most types of labor (as shown in Eberron), because they don't need to be paid for as much as other people do in order to buy the essential things they need to be alive (food, healthcare, clothing, housing, etc). Also would be great in hazardous situations, due to their resistance to poison.
Changling Culture? Shapechanger? Thats the only rule I see.
Well, yeah, but that's literally the whole point of being a Changeling. Being able to change your physical appearance is such a versatile ability that their culture would be absolutely alien to most other races. They can adopt different personalities, live completely separate lives from their different "masks", be excellent con-artists/thieves (they don't need hide their identity while committing a crime because they can just change it at will) or actors, and so on. It's just one rule, but it would have a huge impact on the culture of the race.
Kalashtar Cutlure? Mind Link?
They're telepaths, contain two separate consciousnesses, have advantage on Wisdom saving throws (so are hard to charm/frighten/use Hold Person/Monster on, etc), and don't dream. Not dreaming would certainly impact the culture of the entire race, telepathy would allow them to communicate in an entirely new (and more effective) manner than humans (and other races) can, having two minds gives them a more objective view on reality than other people would have (two heads are better than one, and all), and they're more attuned to "spiritual" aspects of the world.
I dont think I understand your usage of the phrase 'racial mechanics impact ... culture'. I dont see it at all. That isnt to say Eberron has not provided a good culture for these races, maybe they have, but you feel these are enough to derive an entire culture from?
The races of Eberron are certainly impacted by their racial mechanics. At least, quite a few of them are. Warforged culture (if you can call it a culture, given that warforged are so new to the world) is impacted by the race's mechanics and manner of existing (being a constructed race, that is, as Warforged were originally soldiers in the Last War and are now more often indentured servants than anything else). Kalashtar culture is greatly impacted by their psionics. Changelings are a clear example of their culture being impacted by their racial abilities, because of their "racial abilities" basically just being shapechange, which hugely affects who they are. Changelings can have a culture that no other race can possibly have, entirely due to their racial ability to change their physical appearance.
EDIT: Thinking on it as I walk my dog, is this even a goal people want? If there are mechanics which drive a culture, how do you transplant that baseline race, from one setting to another?
They change, based on the setting and its theme. There's more than one way to interpret how any given race's mechanics could impact their culture. Dwarven Resilience could make dwarves more likely to drink a lot of alcohol (because they can effectively drink twice as much as other races without getting drunk), or allow them to live in environments that would make them encounter an abundance of poisons (like in a jungle with poisonous snakes, frogs, and plants). Location would differentiate the same race's culture from setting to setting.
And the lore of the world can do the rest of the work. Kalashtar culture in Eberron is highly tied to the Dreaming Dark and their Inspired thralls in Sarlona oppressing the Kalashtar, causing them to flee to Khorvaire. Kalashtar in any other world would still have telepathy's cultural impacts, as well as their other abilities, but only in Eberron do they have that part of their culture. Same applies to Warforged with the Last War, the Kryn Dynasty races with the Luxon and Dwendalian Empire, and the Mul from Dark Sun.
