I was about to make this suggestion to, it'd be awesome to have a skin library in-launcher to change skins any at time.

+1

There are mods that add this feature directly to the game, wouldn't that be unfair to them?

@Felix14-v2 While there might be, there is also the real possibility that certain mods may not be compatible with others, or available in a mod type or game version, such that they would be able to use one of them.

I say if someone wants to download the mod to allow them to change skins directly in game, then let them. I bet a lot of people would rather have that because it allows them to do it quicker, and in game.

But the problem is:

What TheSenate39 said, about it being incompatible, wrong mod type or game version. Or a mod that becomes abandoned for any reason.

Also, keeping a consistently maintained version of skin changing within the launcher itself, independent to game version or incompatibilities would be more stable and would work for any modpack of any version, since it's external to the game itself.

i was gonna suggest this too, they should really add it so we don't have to open the standalone launcher just to change a skin

It would be perfect here!