Skills, specialization, and artifact effects are located in defaultstats.xdb.
If a value is not present, it is hardcoded in the game's executable files.
You can learn more about the process of editing the executable files here or here, or talk to us on Discord.
Could you explain how to interact with this?
Can I download this and paste it somewhere? (data? or usermods h5u?)

And if I can upload it somewhere, which IDs are free? If you upload a new artifact, where should the link to it be located for the game?