I would propose traits that dwarf could have traits that would affect how they work, build, move, fight...
Each dwarf could have 1 trait when they are "born" or maybe after a specific level. The dwarf could be fast, strong, agile, tough, smart... each one of those would have effect on different actions.
A strong dwarf would deal more damage, dig faster, cut tree faster
A fast dwarf would move faster
An agile dwarf could evade monster hits
A smart dwarf would require less time to perform actions
And also why not put the opposite trait as well and give dwarfs a good and a bad trait.
That way, all dwarf will be different and you would have to look a little bit at their trait to know what they could be used for before transforming them.
I was about to make a similar suggestion, but I was thinking of a more complicated system.
Dwarves could have a number of both born traits and learned traits.
Born traits would be largely random, with the more drastic ones less common.
They could be a large variety of them, and a number of them could be humorous or odd to add flavour to the gameplay.
If dwarf maturity, old age and death are going to pass relatively fast in the game, then it might also be worth making some of the born traits inheritable. Then if you have a dwarf with some traits you don't want to be passed down the gene pool you might be tempted to place that dwarf in the vanguard of your garrison.
Things like:
Easily amused ("This dwarf is almost constantly happy, but their concentration is lacking as a result")
Imbecile ("This dwarf is not well-endowered mentally, but is still capable of performing manual tasks")
Genius ("This dwarf is a natural genius, and particularly skilled with elaborate machinery")
Paranoid ("They're out to get me! I know they are!")
Sociopath ("This dwarf has difficulty empathising with and aiding other dwarves in trouble")
Weak-stomached ("This dwarf has a tendency to faint at the sight of blood")
Pet-lover ("This dwarf loves to be around tame animals, gaining happiness when doing so.")
Charming ("Other dwarves are happy when near this dwarf, and this dwarf has a bonus to fertility")
Gloomy ("This dwarf recevies a small penalty to fertility, and other dwarves are happy to be around them")
Weak liver ("The greatest shame of dwarven society, this dwarf cannot hold their liquor!")
Beautiful ("This dwarf is the epitome of dwarven beauty, and receives a bonus to fertility as a result")
Good-looking ("This dwarf is naturally good-looking, and receives a small bonus to fertility as a result")
Ugly ("This dwarf has a face only its mother could love, and receives a small penalty to fertility as a result")
Naturally artistic ("This dwarf is a naturally skilled artist, but their proficiency at less ephemeral matters suffers as a result")
Hulking ("This dwarf is a physical giant among dwarves, possessing immense physical strength and constitution, but lacking some agility")
Agile ("This dwarf is naturally agile and dexterous")
Gluttonous ("Food and the next meal is constantly on the mind of this dwarf, to the detriment of other activities")
Greedy ("This dwarf likes hoarding as much physical wealth as possible")
Power-hungry ("This dwarf aspires to a high position in dwarf society, and won't let anything get in their way")
etc.
Acquired traits would have a random chance of being acquired by a dwarf when that dwarf does certain actions, or alternatively given after that dwarf has performed an action a certain number of times.
Some of them could also work as skill levels if you want more gradation.
Trained in [weapon] ("This dwarf has developed the know-how to use [weapon] effectively") {chance of attaining when practising with weapon}
(leads to) Skilled with [weapon] ("This dwarf has become skilled with the use of [weapon]") {chance of attaining when dealing damage against enemy with weapon}
(leads to) Master of [weapon]s ("This dwarf is a master of the art of using [weapon]") {chance of attaining when dealing damage against high-level enemy with weapon}
Proficient in [crafting skill] ("This dwarf has learned how to perform [crafting skill]")
Experienced in [crafting skill] ("This dwarf is a skilled [crafting skill]")
Master at [crafting skill] ("This dwarf has turned [crafting skill] into a fine art form).
etc.
And some which could be acquired either way, e.g.:
Solidly built ("This dwarf has a deal of natural physical strength and constitution")
Disfigured ("This dwarf has a horrible facial disfigurement, and receives a large penalty to fertility as a result, but some weak enemies will flee at its sight")
Limp ("This dwarf walks with a limp")
Blind ("This dwarf is blind, a significant hindrance in many physical activities, but it does have a better chance of detecting hidden or invisible enemies")
Frightened of X [where X is a creature type] ("This dwarf has a deeply embedded fear of X, and is liable to flee at the sight of one") {chance of attaining when badly injured by X}
etc.
The most significant traits could also be attached as epitaphs to names, so that it is easy to tell a dwarf has it at a glance. E.g. 'Thoren Gilgirn "The Lame"'.