Rain Particle random start

I have an asset that i downloaded that is for rain that uses this code

 var burstEnergy : float = 10.0;
 var explosionObject : Transform;
 
 function LateUpdate () {
     var theParticles = particleEmitter.particles;
     var liveParticles = new int[theParticles.length];
     var particlesToKeep = 0;
     for (var i = 0; i < particleEmitter.particleCount; i++ )
     {
         if (theParticles[i].energy > burstEnergy)
         {
             theParticles[i].color = Color.yellow;
             // We have so much energy, we must go boom
             if (explosionObject)
                 Transform.Instantiate(explosionObject, 
                     theParticles[i].position,  
                     Quaternion.identity );
         
         } else {
             liveParticles[particlesToKeep++] = i;
         }
     }
     // Copy the ones we keep to a new array
     var keepParticles = new Particle[particlesToKeep];
     for (var j = 0; j < particlesToKeep; j++)
         keepParticles[j] = theParticles[liveParticles[j]];
     // And write changes back
     particleEmitter.particles = keepParticles;
 }    

How can i make this particle start randomly. Also how do i make the skybox change from the sunny day to a different skybox?

Thanks!!