I got it!!!
Go me, ok heres the code:

Ball[] bBalls;
int MAX;
int ch;
float d;
color c = color(0,0,0,random(255));
int n;

void setup()
{
 size(1024, 730);
 //frameRate(25);
 background(20,10);
 smooth();

 MAX = 1000;
 ch = 0;

 bBalls = new Ball[MAX];

 for (int i=0;i<MAX;i++)
 {
   bBalls[i] = new Ball();
   bBalls[i].x = random(0, 1024);
   bBalls[i].y = random(0, 730);
   bBalls[i].vx = random(3,5);
   bBalls[i].vy = random(-4,4.25);
   bBalls[i].d = d+i;
   bBalls[i].c = color(255,0,0);
   bBalls[i].c2 = color(0,255,255);
   bBalls[i].z = i-.8 /0.08;
   bBalls[i].fil = c;
   n=i;
 }
}

void draw()
{
 for (int i=0;i<ch;i++)
 {
   bBalls[i].run();
 }
}

class Ball
{
 float x;
 float y;
 float vx;
 float vy;
 float d;
 float z;
 color fil;
 color c = color(255,0,0,random(100));
 color c2= color(0,255,255,random(100));

 void run()
 {

   if (key == '1'){
     bBalls[2].d=50;
     c = color(10,10,10,random(100));
   }
   else if (key == '2'){
     d = 10;
   }

   drawShape();
   x = x + vx;
   y = y + vy;

   if (x < 0 || x > width)
   {
     vx = -vx;  
   }
   if (y < 0 || y > height)
   {
     vy = -vy;  

   }
 }

 void drawShape()
 {
   ellipseMode(CENTER_RADIUS);
   strokeWeight(1);
   noFill();
   //fill(0,100);
   stroke(c2);
   ellipse(x, y, d, d);
   fill(fil);
   stroke(c);
   ellipse(x+z,y,d,d);

 }
}

void mousePressed()
{
 ch = ch+1;
}

---------------------------------------
The magical cure was to add the:
   
   if (key == '1'){
     bBalls[2].d=50;
   }
   else if (key == '2'){
     d = 10;

...In the void run(), the '1' key changes only the second ellipse, while the '2' key will change all of them.
Good times.