The short version is that a Changeling can shapeshift to a form that can produce sperm to impregnate someone, and can shapeshift to a form with a uterus and eggs to get pregnant, but a pregnant Changeling cannot shapechange to a form without a uterus without ending the pregnancy.
Changeling Reproduction
If a changeling with the Racial Emulation feat matches its subtype to that of a partner, a child resulting from the union will always be of that humanoid subtype. If a changeling in a female form conceives a child, she loses the ability to change her gender until after the child is born.
Two changeling parents breed a changeling child. A changeling and a humanoid can mate to produce an offspring with the child having a 50% chance to be of either race. Your question noted that there's a 50/50 chance of getting a changeling if they mate with a human...but it's not just human.
In the Worlds of Star Trek: Deep Space Nine novella Olympus Descending, Odo learns from an elder Changeling that there are no "infant" Changelings, but just Changelings that are kept separate from the rest of the Great Link, as Changelings cannot reproduce since the departure of the ancient Progenitor centuries ago; ...
Having said that: while changelings CAN mate with other humanoids, I'd say that it is RARE for them to impregnate creatures of other species. It can happen, but the fertility rate isn't that high. It's quite possible that humans and other human-compatible species are the most viable. With that said…
"A human child might be taken due to many factors: to act as a servant, the love of a human child, or malice. Most often it was thought that fairies exchanged the children.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
The Changelings were sent to retrieve Picard's body so that they could specifically remove parts of his parietal lobe—the part that was supposedly defective from Irumodic Syndrome.
Are they biologically asexual and just choose their current sex with shapeshifting? Yes. What's been stated in the past is that changelings set their sex with shapeshifting.
As crew members beamed on and off their ships, the computers recognized this new genetic code as "common biology" and integrated it into the DNA of every officer in the fleet. The Changelings wanted Jack because of they needed his Borg-altered DNA, though they later ended up acquiring this from Picard's body.
A changeling can't make the wings at all. If they had wings, like from a class feature or something, then they could look like an Aaracokra with wings because they will have those limbs at that point.
Most changelings don't know they're changelings.
Though they may always feel somewhat different or removed from human life, most changelings are too young to understand who they truly are.
Changelings reach maturity slightly faster than humans and live as long as humans do, typically about 100 years.
Changelings have red blood like a majority of the other races. Bleeding around others may alert many that the Changeling is not of the same race (should the blood color vary). For this reason, a Changeling will usually choose to take the form of a race with red blood.
The short version is that a Changeling can shapeshift to a form that can produce sperm to impregnate someone, and can shapeshift to a form with a uterus and eggs to get pregnant, but a pregnant Changeling cannot shapechange to a form without a uterus without ending the pregnancy.
Changelings are typically born with female anatomy, but some prefer to maintain male primary and secondary sex characteristics once in control of this ability.
Changelings have the unique ability to transform their body to look however they want, provided they keep the same arrangement of limbs they already possess. It is very rare to actually see a changeling in it's 'true' appearance. Even when disguised, changelings can instinctively recognize each other.
The true form of a changeling is a bit paler than a typical human with slightly elongated limbs. Their eyes are colorless and ringed by black as pictured in the artwork above by Julia Zhuravleva. They have no body hair, but the hair on their head can be platinum, white, or silver.
Unlike ponies, changelings do not have cutie marks.
By RAW changelings revert when they DIE but not when they are unconscious (it would be hard to maintain a long term masquerade if you revert when you sleep!).
Changelings typically have large eyes with narrow pupils, ranging in color from white, to yellow, to black. Hair colors are similar: Light grey, platinum blonde, shades of silver, all the way to the darkest hair color being a light brown.
Star Trek: Picard Season 3 firmly established Jack Crusher as a significant character within the beloved franchise, placing him alongside the iconic figures of the series. As the son of the esteemed Jean-Luc Picard and Beverly Crusher, Jack (Ed Speleers) plays a crucial role in the Star Trek canon.
Obviously, a changeling's appearance can change at any moment, but they do have a true form. Their true skin is usually grey or pale white, and their facial features are blank slates to an unnerving degree. They're typically thin and gaunt, and their hair is usually silvery with an occasional green or pink tint.
according to the rukles for changelings: Languages: Changelings begin play speaking the primary language of their host society and Common. Changelings who have high Intelligence scores can choose from among the following bonus languages: Aklo, Draconic, Dwarven, Elven, Giant, Gnoll, Goblin, and Orc.
Sometimes changelings are old, nasty fairies who revel in the sorrow they cause; or fairies with prodigious appetites for human food or mortal breast milk. Sometimes the changelings are fairies so old and worn out that their kinfolk have left them behind, happy to be rid of them in exchange for a plump human child.