An interesting way to make weapons have two fire modes: 

Some have discovered a hidden weapon in Scourge, which is piggybacked on the player's mothership. Its attack pattern is as follows: When the player presses the button for a certain amount of time, fire Ammunition A, otherwise fire Ammunition B.

Here's how to do it: 

We need some way to distinguish "whether the player pressed the button for a certain amount of time, which can be solved with a "Controlled" weapon (WeaponClass = 1) (fragmentation bomb and firework use this WeaponClass). This type of weapon can trigger "Detonated" (Condition = 6) when the player releases the bullet. We add it to a detection Ammunition and set it to generate Ammunition B. And we can set another Expired (Condition = 5) to generate Ammunition A.

Next, make sure the detection Ammunition remains attached to the barrel throughout the process. This requires Type to be set to 3 (interestingly, Bullet's Shape must be 2, otherwise it will have some kind of deviation and jitter)

The framework is as follows:

{
  "ItemType": 25,
  "Id": /*id*/,
  "Body": {
    "Type": 3,
    "Lifetime": /*certain time*/,
    "BulletPrefab": /*a Bullet which Shape is 2*/
  },
  "Triggers": [
    {
      "Condition": 6,
      "EffectType": 2,
      "Ammunition": /*Ammunition B*/
    },
    {
      "Condition": 6,
      "EffectType": 3
    },
    {
      "Condition": 5,
      "EffectType": 2,
      "Ammunition": /*Ammunition A*/
    }
  ],
  "ImpactType": 1
}