LocalRockEater

On hatching, the horns are covered with a layer of mostly-hairless skin. The bone here is sturdy enough to serve a similar function as an eggtooth, but is still developing along with the rest of the skull. It will remain soft and somewhat malleable for the few few months to a year of life. The skin covering will die and be replaced with keratin of the same color when the horns are fully developed in late adolescence.

It's easy to affect a horn's development when soft, either accidentally or deliberately. Something as simple as a hatchling spending too much time leaning on one side can train a horn to grow in a "wrong" direction. Some cultures will go to great lengths to correct bent or asymmetrical horns, while others don't consider it a big deal as long as it doesn't affect the hatchling's health. Horns that are severely asymmetrical or curved in a very atypical way (straight forward, for example) can cause neck issues, problems balancing, or even cause stress or injuries to the rest of the skull.

On the other hand, some cultures consider it normal to deliberately sculpt a hatchling's horns. This can be done for purely aesthetic reasons or as a clan/family identifier. The latter is most common in very traditionalist Tundra communities in the Southern Icefield, where it is a very old practice, and is almost never seen in northern flights or mixed-breed communities. Folklore has it that it began as a way to recognize clanmembers in storms strong enough to blow away scent - skeptics say that visibility in a storm like that would be too low to see someone's horns at a distance anyway. The former is highly controversial for being fully elective, so to speak, and Tundras who practice traditional horn modification see it as deeply weird and kind of cruel to saddle your kid with a horn shape that won't be shared with anyone else.

All stances are controversial to someone, and medical opinion is mixed on whether "standard" horn shapes are inherently healthier than just letting them grow, whether deliberate modification is necessarily harmful, when it's justifiable, and how much is too much. Add in the fact that any procedure is irreversible and can only be done when the hatchling is too young to say yes or no - it's a mess.

On the fur front, a hatchling's "baby coat" is waterproof, thin, and extremely soft. Its purpose is to keep the egg liquids away from the skin and protect them from the cold just long enough to crawl under the closest parent. Adult Tundra fur is not waterproof; it keeps them dry by being thick and heavy enough that snow or liquid simply doesn't make it to the skin. A hatchling will start growing their adult coat almost immediately after making it out of the egg, and sheds their baby coat within a couple of days.