Issue in detail:
Let say we have 4 major tasks: A, B, C, D such that following combinations are considered valid:
1) A->B->C->D
2) A->C->D
3) A->B->C
4) A->D
 and so on.

On top of that, we would like to allow users to customize the flow of tasks as following:
1) A->myOperations->D
2) A->preTaskDoperations->D->postTaskDoperations.


Currently, I have support for user flow without this customization like 
1) A->B->C->D
2) A->C->D
3) A->B->C
4) A->D
 and so on.
Note: same was mentioned above earlier.

##</code><code>##

<!--Make an xml file something like below-->
<xmlFile>
	<action name="A" execute="true">
	</action>
	<action name="B" execute="true">
		<arguments>
			<arg name="endToEnd" value="true"/>
		</arguments>
		<preTasks>
			<!--thinking of making this as text-->
			$ENV{skipActions}='true';
			makeAServerdown();
			<!--this can be later executed with exec function-->
		</preTasks>
		<postTasks>
			checkBServer();
		</postTasks>
	</action>
</xmlFile>

##</code><code>##

Object Oriented approach.
1) make code file which has such customized details. (derived class)
2) provide override mechanism to end user. 
3) support flow of tasks like mentioned in xml but remove perl code from there. There are several alternatives to do this which maybe as simple as reading properties file.