They can be added into the public torishop by the item forgers or you can get your own unique item exclusively added for $$

Basically what imp said, if you create an item you can submit it to me and if it meets the requirements it can be added to the shop, but this isn't a guarantee by any means. Alternatively, if you want the item exclusively for yourself you can talk to Icky and get it added to the game for yourself to have in exchange for $$, but you will need the obj file already created, Icky will not create the actual object itself for you, he will just add it to the game.

If you are referring strictly to the steps in this thread, and you add the obj yourself to your game files, that will only be client-side.