For example, I have 2 Lifelines ClassB, ClassC.

ClassB has "sendMessage" to Class C.
also, ClassB has "composeMessage" to itself.
composeMessage in ClassB has sendMessage to Class C.
This is my existing diagram.

Now, I want to modify it, I add a lifeline before ClassB called ClassA.

ClassA has a message "initialize" to ClassB before ClassB.sendMessage() and ClassB.composeMessage()

I can easily move ClassB.sendMessage() to the lifeline of ClassB inside "initialize" but I am having difficulty in moving ClassB.composeMessage() [that has already ClassB.composeMessage().sendMessage() ] to inside "initalize".

composeMessage() originally has Source and Target lifeline set to ClassB (being a self-message). If I change the Target lifeline to ClassC temporarily, I can easily drag the Source lifeline to the "initalize()" and then drag Target lifeline of composeMessage() back to ClassB inside "initalize()" (making it a self-message again) but it leaves an EMPTY LIFELINE in ClassB where the composeMessage().sendMessage() used to be. to sum it up, I only moved composeMessage() without it contents. I want to move it to "initialize()" with all it's contents intact.

Is this possible? How?

For the sake of discussion, imagine an already large diagram and composeMessage() actually has a lot of nested messages to many lifelines as well.