Particles from a Later-Loading Pack

You want your weapon to show the I_Fire_Blue particle, but the particle system that defines it ships in a separate pack that loads after yours. Done naively, your item asset resolves before the particle exists.

Goal

• Your item displays the I_Fire_Blue particle.
• The particle system itself lives in a different pack (Riprod:Hexcode) that loads after your item asset, defined at Server/Particles/.../I_Fire_Blue.particlesystem.
• The stock particles already on the item stay intact.

The key fact: particle systems are .particlesystem files and are NOT patchable. Patchly only patches .json. What you patch is the .json item asset that REFERENCES a particle by its SystemId string. The string is resolved against the registered particle systems at merge time.

The Asset

Server/Item/Items/Weapon/Sword/Template_Weapon_Sword.json

{
  "TranslationProperties": {
    "Name": "server.items.Template_Weapon_Sword.name"
  },
  "DroppedItemAnimation": "Items/Animations/Dropped/Dropped_Diagonal_Left.blockyanim",
  "Model": "Items/Weapons/Sword/Iron.blockymodel",
  "Texture": "Items/Weapons/Sword/Iron_Texture.png",
  "Icon": "Icons/ItemsGenerated/Weapon_Sword_Iron.png",
  "PlayerAnimationsId": "Sword",
  "Reticle": "DefaultMelee",
  "Quality": "Template",
  "ItemLevel": 15,
  "Categories": [
    "Items.Weapons"
  ],
  "IconProperties": {
    "Scale": 0.35,
    "Translation": [
      -22,
      -22
    ],
    "Rotation": [
      45,
      90,
      0
    ]
  },
  "Utility": {
    "Compatible": true
  },
  "Interactions": {
    "Primary": "Root_Weapon_Sword_Primary",
    "Secondary": "Root_Weapon_Sword_Secondary_Guard",
    "Ability1": "Root_Weapon_Sword_Signature_Vortexstrike"
  },
  "Tags": {
    "Type": [
      "Weapon"
    ],
    "Family": [
      "Sword"
    ]
  },
  "Weapon": {
    "EntityStatsToClear": [
      "SignatureEnergy"
    ],
    "StatModifiers": {
      "SignatureEnergy": [
        {
          "Amount": 20,
          "CalculationType": "Additive"
        }
      ]
    }
  },
  "ItemAppearanceConditions": {
    "SignatureEnergy": [
      {
        "Condition": [
          100,
          100
        ],
        "ConditionValueType": "Percent",
        "Particles": [ // you want to ADD one particle entry to this array
          {
            "SystemId": "Sword_Signature_Ready",
            "TargetNodeName": "Handle",
            "PositionOffset": {
              "X": 0.8
            },
            "TargetEntityPart": "PrimaryItem"
          },
          {
            "SystemId": "Sword_Signature_Status_Spawn",
            "TargetNodeName": "Handle",
            "PositionOffset": {
              "X": 0.5
            },
            "TargetEntityPart": "PrimaryItem"
          },
          {
            "SystemId": "Sword_Signature_Status",
            "TargetNodeName": "Handle",
            "PositionOffset": {
              "X": 0.55
            },
            "TargetEntityPart": "PrimaryItem",
            "Scale": 1.3
          }
        ],
        "FirstPersonParticles": [
          {
            "SystemId": "Sword_Signature_Ready",
            "TargetNodeName": "Handle",
            "PositionOffset": {
              "X": 0.8
            },
            "TargetEntityPart": "PrimaryItem"
          },
          {
            "SystemId": "Sword_Signature_Status_Spawn",
            "TargetNodeName": "Handle",
            "TargetEntityPart": "PrimaryItem",
            "PositionOffset": {
              "Y": -100
            }
          },
          {
            "SystemId": "Sword_Signature_Status",
            "TargetNodeName": "Handle",
            "PositionOffset": {
              "X": 0.5
            },
            "TargetEntityPart": "PrimaryItem"
          }
        ],
        "ModelVFXId": "Sword_Signature_Status"
      }
    ]
  },
  "ItemSoundSetId": "ISS_Weapons_Blade_Large",
  "MaxDurability": 80,
  "DurabilityLossOnHit": 0.21
}

SystemId is a string id. A stock system it names lives at Server/Particles/.../Sword_Signature_Ready.particlesystem; the one you want to add, I_Fire_Blue, lives at Server/Particles/.../I_Fire_Blue.particlesystem inside the Riprod:Hexcode pack.

The patch

Goes at the item's path with .json swapped for .patch. Use Particles+ to APPEND your reference into the existing condition's array instead of replacing the stock particles. $Requires keeps the reference out until Riprod:Hexcode is actually present.

{
  "$Requires": "Riprod:Hexcode",
  "ItemAppearanceConditions": {
    "SignatureEnergy": [
      {
        "Particles+": [
          {
            "SystemId": "I_Fire_Blue",
            "TargetNodeName": "Handle",
            "TargetEntityPart": "PrimaryItem"
          }
        ]
      }
    ]
  }
}

Adjust the condition key (SignatureEnergy here) and the entry shape to match the real asset you are patching. The point is the + suffix: it appends a reference without wiping what is already there.

After

• The SignatureEnergy condition's Particles array now holds both the stock Sword_Signature_Ready entry AND your I_Fire_Blue entry.
• The stock particle survives because Particles+ appends rather than replaces.
• The merged item is written after Riprod:Hexcode registers, so by the time the asset resolves, the I_Fire_Blue system already exists and the SystemId string resolves.

Why the load order works out: Patchly re-runs its merge on every AssetPackRegisterEvent. When Riprod:Hexcode registers, the merge re-runs and the merged item is (re)written with I_Fire_Blue present. $Requires: "Riprod:Hexcode" means the reference is skipped on any earlier pass when Riprod:Hexcode is not yet loaded, so you never write a dangling SystemId.

Notes

• You CANNOT patch the .particlesystem file itself (yet). It is not JSON. If the particle system does not exist in any pack, ship its .particlesystem as a NORMAL full asset file in your pack. Patchly only wires the JSON reference to it.
• The same rule applies to models (.blockymodel), textures (.png), and lang (.lang): patch the JSON that REFERENCES the binary asset, never the binary asset. Ship those as normal full files.
• Use Particles+, not Particles, unless you genuinely intend to drop the stock particles. A bare Particles array REPLACES the whole array. See the syntax reference for the append rules and Removing Values for deletion.
• Use $Requires whenever your patch names an id that only exists once another pack is loaded. It guards against writing references the engine cannot resolve yet. Full meta-key reference is in the syntax reference.