Perhaps you can explain what you are trying to do. Often, people ask things that are technically hard, because they think of one solution, while they might have overlooked simpler solutions...

I demonstrated how to mix sketches (kind of) in http://bazaar.launchpad.net/~philho/+junk/Processing/files/head:/_SmallPrograms/DrawingInSequence/ but it is a bit advanced as example, and perhaps not addressing your need. But it also shows how to time the run of a sequence, and to chain such runs, just using millis().

Mmm, OK, here is a simpler sketch, perhaps closer of what you shown in a previous thread:

1. int startTime;
2. int step;
3. int firstStepTime = 2000;
4. int secondStepTime = 3000;
5.  
6. float cx, cy;
7. float count;
8. color initialColor = #BBCC00;
9. color circleColor = initialColor;
10. int circleSize = 100;
11. float circleStep = PI / 150;
12.  
13. void setup()
14. {
15.   size(512, 512);
16. }
17.  
18. void draw()
19. {
20.   background(255);
21.   if (step == 0)
22.   {
23.     if (millis() - startTime >= firstStepTime)
24.     {
25.       // Change color every 2 seconds
26.       circleColor = circleColor == initialColor ? #DDEE00 : initialColor;
27.       startTime = millis();
28.     }
29.   }
30.   else if (step == 1)
31.   {
32.     if (millis() - startTime >= secondStepTime)
33.     {
34.       // Change color after 3 s
35.       circleColor = #DD5500;
36.     }
37.   }
38.   showCircle();
39. }
40.  
41. void showCircle()
42. {
43.   cx = width / 2 + 200 * cos(count);
44.   cy = height / 2 + 200 * sin(count);
45.   count += circleStep;
46.   noStroke();
47.   fill(circleColor);
48.   ellipse(cx, cy, circleSize, circleSize);
49. }
50.  
51. void mouseClicked()
52. {
53.   if (dist(mouseX, mouseY, cx, cy) < circleSize / 2)
54.   {
55.     step = 1;
56.     startTime = millis();
57.     circleStep = -circleStep;
58.     circleColor = #BB5500;
59.   }
60. }

As you can see, one can change the behavior of the sketch (I could have put showCircle in step 0 and called another function in step 1) based on time and / or user interaction.

In Java / Processing, calling another program is a bit clumsy, it is easier / faster to modularize the program, and call the appropriate section when the need arises.

Just reset the relevant variables. In my case, that would be step and startTime, and perhaps circleStep and circleColor as well.
You can put the code putting these variables at an initial value in a function, so you can call it from various places of your code.