Change particles alpha / sharedMaterial

I have two different issues with particles and I have trouble in both of them.

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First issue - dissolve a particle

I have a particle effect that is a gameobject group that consists of 4 different legacy particle systems (emitter+animator+renderer). I need to smoothly dissolve it using opacity.

First thing I do is I stop all emmitters. And that works ok.

 for (var c: Component in fx.GetComponentsInChildren(ParticleEmitter)) {
     var pe: ParticleEmitter = c as ParticleEmitter;
     pe.emit = false;
 }

But then I'm trying to affect the alpha of emitted particles and that's where I fail:

 for (var c: Component in fx.GetComponentsInChildren(ParticleEmitter)) {
     // I've tried trough particle emitter:
     var pe: ParticleEmitter = c as ParticleEmitter;
     var pr: Particle[] = pe.particles;
     for (var i: int = 0; i < pr.Length; i++) {
         pr[i].color.a = new_alpha;
     }
     
     // I've also tried through particle animator:
     var pa: ParticleAnimator = c as ParticleAnimator;
     for (var i: int = 0; i < pa.colorAnimation.Length; i++) {
         pa.colorAnimation[i].a = new_alpha;
     }
 }

So, I need to change alpha of emitted legacy particles and don't know how to do that.

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Second issue - shared particle material

This is not connected to 1st issue. Here are different particles.

So, I have a bunch of particles that use the same material. And when I'm running my game in editor and use inspector to change that material's color - it works fine and affects on all particles on the screen.

But I can't to do that using code.

I've tried to get a shared material from one of my particles and to change it:

 var material: Material =
     particle_go[0].GetComponentInChildren(ParticleSystem).renderer.sharedMaterial;
 // material is not null here!
 material.color = new_color;

How do I change the shared material just as I do when changing "color" property in inspector?