Some concerns:
1) are you suggesting reading this : "task=B pretask=makeAServerdown posttask=checkBServer" from some text file. or hardcoding in code? I am assuming text file for now.

2) The customizations suggested by you will work if only known action is being called. But my use case is that user can customize with anything they like i.e. they can maybe add any code block they want etc.
 example of code block: (simple example here)

for (int i=0;i<10;i++) {
print('just a block for fun: ' . $i . "\n");
}