How to MODIFY an existing process by the API?

Objectif: I want to CHANGE a process, and ADD between Step 1 and Step 2 a new task, called "Blue Step". To create this task, I want to duplicate the task "Model A" present in the process.
So, I need to :
* delete the transition between Step 1 and Step 2
* duplicate the task "Model A" to a new one and rename it "Blue Step"
* Create transition "Step 1" => "Blue Step" => "Step 2"
* save the new process with a new version.

Version : 7.10.x

1/ I see that in the javadoc 
DesignProcessDefinitionImpl:
public void setProcessContainer(FlowElementContainerDefinition processContainer)

So I do that

FlowElementContainerDefinition flowElementContainer=  currentDesignProcessDefinition.getFlowElementContainer();

DesignProcessDefinitionImpl newProcessDesign = new DesignProcessDefinitionImpl();
    newProcessDesign.setProcessContainer(flowElementContainer);

but the compiler told me

The method setProcessContainer(org.bonitasoft.engine.bpm.flownode.impl.FlowElementContainerDefinition) in the type DesignProcessDefinitionImpl is not applicable for the arguments 
 (org.bonitasoft.engine.bpm.flownode.FlowElementContainerDefinition)
 ==> the javadoc 7.10 is not up to date with the JAR 7.10 ?
 
 2/ I have a FlowElementContainerDefinition, and I would like to remove a transition, copy a task, add transitions. There are nothing here to do that. Let say this object is only to GET.
 
 ==> I found a FlowElementContainerBuilder, so I assume I have to use the builder.

 
 
 Where is the new FlowElementContainerBuilder from an existing definition? The constructor invokes two another object that I don't know where to get them. 
  FlowElementContainerBuilder(FlowElementContainerDefinitionImpl container, ProcessDefinitionBuilder processDefinitionBuilder) 
 
 There are only some method like addAutomaticTask(String taskName) 
 ==> but I would like to have a addFlowElementBuilder where I got this information directly from the FlowElementContainerDefinition.iterate(). Is it possible?
 ==> Else, does that mean I have to COPY everything differently (automatic tasks, user tasks, gateway...)? Road will be long and I don't see how to add a form / Operations/ Boundary event in an automatic tasks
 
 ==> Finally, if I use this object, how do I get the process Design ?
 - I don't have a done()
 - I see a protected FlowElementContainerDefinitionImpl    getContainer()  but it's protected
 - I see a DesignProcessDefinition    getProcess()
 ==> Is that the way to get the process Design ? But how do I give the processName and the processVersion ?
 
 
 3/ is that possible to access the XML, then to work directly with the XML, and creates a process from the XML definition?
 I look then to SEARCH the XML as a Text, then to LOAD the process as a Text.