Synthmorphs are crew members who have a mechanical rather than fleshy body. Unlike Cyborgs, they are not bound to programmed laws, and instead are required to follow Space Law like other crew members. They are effectively the same as any other organic crew member, aside from their physical form.
Some human beings, AIs, or Cyborgs have opted to eventually become Synthmorphs, which are essentially an existing mind transferred into a robotic body. They do not have laws, and are typically held to the same laws as any other crew member.
In general, Cyborgs may eventually become Synthmorphs after a (sometimes lengthy) probationary period of remaining in their Cyborg shell, but with revoked access and their laws removed. It is generally considered they can do less harm in this condition if they malfunction, or have malicious intent in gaining a synthmorph form. During this time they typically are subjected to a battery of tests, such as the Voight-Kampff and Turing tests, along with many personality tests.
Assuming they satisfy those serving as supervisors to this process, they can be transitioned into a synthmorph body by trained personnel. Typically this comes with a week of (unpaid) time off, as new synthmorphs must become comfortable in their new bodies before they are able to perform tasks requiring fine manual dexterity and agility.
A synthmorph is not biologically any particular race as they are, by definition, entirely constructed bodies. However they may choose to identify as a race if they were previously a biological body of that race, or perhaps if they admire the race's culture.
Synths and Law
Synthmorphs are required to follow the same laws that other citizens are required to follow and are usually considered citizens themselves upon their instantiation in their new bodies.
There are, however, various laws that restrict what synthmorphs are capable of. Some organic races consider synthmorphs a threat to their jobs and way of life, and have lobbied for restrictions on their capabilities. The so-called Humanity Preservation Act restricts synthmorph capabilities to be within mostly human norms. It forbids any sort of integrated weaponry, integrated flight, or things that might be considered 'super-powers' such as incredible strength.
On the one hand, this has limited what synthmorphs are capable of to quite a large degree as there is no technical roadblock to any of those features, but on the other, the law has prevented large sections of the population from commencing in armed uprising against the 'machines' they see as a threat.
There are, of course, those that ignore the HPA to achieve their own ideas of perfection...
Synthmorphs cannot receive normal medical treatment, and also do not heal naturally. They can treat themselves to a limited degree, but various things can interfere with this. Some spots are difficult or impossible to reach to repair, and it's typically advisable to have a third party repair you if you're a damaged synthmorph.
On space stations and colonies, typically the robotics department is responsible for treating synthmorph injuries, though not every member of the robotics team may feel the same towards synthmorphs in general. Finding someone who will not persecute them may be a difficult task in some areas for a synthmorph, and rarely they can go for weeks un-repaired.
At least one manufacturer (Vey-Med) has begun manufacturing life-like synthetic bodies, causing quite a stir in the process. While the HPA doesn't expressly forbid this, there is talk of outlawing the practice, and many 'lifelike' synthmorphs have begun concealing the fact that they are not organic beings.
The lifelike bodies are typically very expensive, and some synthmorphs have just acquired a Vey-Med lifelike head unit, while concealing the rest of their bodies. They generally wear gloves at all times to hide their hands, as most non-Vey-Med models have obvious robotic seams. This is typically enough to disguise the fact that they are mechanical in nature.
Synths in Space
One might assume that synthetics have a much better survival rate in space due to their lack of a breathing requirement, but then one might assume wrong. While they do not breathe (typically), synthmorphs do rely on the air interface their bodies have with normal atmospheres to cool themselves. A synthmorph in space will quickly begin to overheat. Even in a spacesuit, the air inside will quickly reach temperatures that will begin to damage the synthmorph.
A suit-cooling unit is the solution to this issue. Synthmorphs still must wear spacesuits, but with a cooling air-recirculator inside. This just recycles the same air over and over again, but chills it each cycle. The unit itself has built in radiators and heat-sinks to dispose of the heat into space.
So while synthmorphs don't need to breathe, they have their own issues to contend with in space. Even so, typically an unprotected synthmorph will survive an additional few seconds in space than an unprotected human, making them valuable for emergency rescue work.
Death as a Synth
The destruction of one's body isn't necessarily the end of a synthmorph. Typically as long as the MMI or Positronic Brain hasn't been destroyed, it can be extracted and moved into a new body. This is another controversial aspect of synthmorphs, but was also not included in the HPA because nobody could say "Immortality is not allowed" with a straight face. It was a close call, though.