In order to import your own skins into the mod, you only need to take your skin files and place them in the appropriate folder.
In order to use skins with the mod, it is important that they are in the correct skin format (64×64) and not the pre-1.17 format of 32×64
For Alex skins, they would go into MINECRAFT_INSTANCE/Regeneration Data/Alex
For Steve skins, they would go into MINECRAFT_INSTANCE/Regeneration Data/Steve
Note: MINECRAFT_INSTANCE is the location where you have your Minecraft install. This would usually be one directly back from your mods folder.
When the mod launches, it downloads a set of skins from my GitHub repo and another set of skins from https://namemc.com. The skins from namemc are always random and are from the trending tab of the website and a collection of skins you have worn in the past that namemc has collected on you. The skins downloaded from my GitHub repo are a large collection of Doctor Who related skins.
These options are optional and can be disabled in the client config of the mod.
To disable namemc trending skins, you must set “downloadTrendingSkins” to false in “regeneration-client.toml”
To disable namemc past skins, you must set “downloadPastSkins” to false in “regeneration-client.toml”
To disable the Doctor who related skins, you must set “downloadInternalSkins” to false in “regeneration-client.toml”