1. is it possible to make the skins common, rare and so on and then draw them less often?

2. easier way to add skins for example by /skin add STEAMID and then load the data into the database.

3. simply delete skins instead of blacklist, e.g. by /skin delete STEAMID

1) The database contains almost 75,000 skins, so it's not possible to just automatically assign them all to "common" or "rare".
Do you mean ability to boost the likelyhood of a skin appearing in a certain skin pack?   So for example "Bronze Skin Pack should have a 50% chance of receiving one of these skins [...]"?

2) The database already contains all the skins.  If you want to update it to with latest skins then just run skinshop.builddatabase

3) You can type skinshop.blacklist.id STEAMID to delete a skin.  (If you want to rename the command just use a bind)

I dont want to use all available workshop skins.. i only want to implement 5-10 for each kategorie and put in manually a rare-mod

So replace blacklist with a whitelist basically?  So that only specific list of skins that you manually added to config are available?

Yeah that would be great.. e.g. /skin add WORKSHOPID and then the plugin will download the skin