Hello,
Isn't there a command for an admin to erase everything in the store ?  Then I just want to add some items that we can't find for sale or that we can't craft. And also add commands from some mods.

All you have to do is go into the config file and delete anything you don't want from them from the items list.
Or simply disable the default provided shops and create new ones. 

    "Commands": {
      "DisplayName": "Commands",
      "DisplayNameColor": null,
      "Description": "You currently have {0} coins to spend in the commands shop",
      "DescriptionColor": null,
      "Permission": "",
      "Currency": "",
      "CustomCurrencyAllowSellOfUsedItems": false,
      "CustomCurrencyNames": "",
      "CustomCurrencyIDs": 0,
      "CustomCurrencySkinIDs": 0,
      "EnabledCategory": true,  < set to false to disable the shop entirely.
      "EnableNPC": false,
      "NPCId": "",
      "NpcIds": [],
      "Items": [
        "Minicopter",   < or remove / add items here from the shops
        "Sedan",    
        "Airdrop Call"
      ]
    },​