Is this possible? It gives more freedom and takes away work from the admin that has to add thousands of skins.

Thank you for your suggestion. Could you please provide me more ideas on that? Because I am not sure how should I implement that. I mean, how should it work. They add only for themselves or for everyone skins? What if they add "invalid" skins? Or something

i would also be interested. 4 me i would suggest to have user specific skins. i want my players to use custom/own skins but don't want to add every one of them and at the same time share it with all others on the server. a secondary command to change an item to a specific skin would be awesome. something like /reskin box.wooden.large [steam community id] or just /reskin [steam community id] with the plugin checking the inventory and just changing the item in the inventory to the specific skin. 

I'll take a look at it. Thank you for your suggestion.

many thanks in advance. i would also support you if needed. perhaps you need to have another/custom command to avoid collisions with other skin plugins as some already use the /reskin command. e.g. https://umod.org/plugins/item-skin-randomizer which already changes just specific inventory item but to a random and no custom id.

Merged post

just got another idea/possible solution. perhaps you can just add something like a filter with global added skins (all skins added by users with the "skins.admin" permission and skins added by users with "skins.addcustomskin" permisson who get a custom flag/variable in config array with the respective user id who are just shown additionally to the global skins in the container when you are the respective user