The 'putting mugs ect. on tables' is already done in the game.
Its done by setting an item to not rot and putting it using the mapeditor. If you have a guildhall you'd like to decorate in that manner, feel free to ask a mapper.
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As for the second, it won't work. Again if the server reloads/crashes you lose everything.
If the server restarts and the mana potion vendor (say) had 0 potions, as soon as the restart happens he'll have his max.
And killing NPCs is impossible, NPCs do not work like monsters.
Semi public storage
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