Maybe it's a little bit late, but since I've been struggling with this, I'm posting it just in case it can help anyone.
If you just want to change the actual label of the current page, the easiest way to do it is in this way:
$this->view->navigation()->findOneByRoute(
Zend_Controller_Front::getInstance()
->getRouter()
->getCurrentRouteName()
)
->setLabel($label);
The findOneByRoute will work charmly if you use Zend_Routes, if you don't, you can change it by findOneByX, being X is any property of the page.
Answering to the question of the OP, in this case, it would be easy to do:
$this->view->navigation()->findOneByLabel('Collaborators')
->setLabel('Collaborator'. $name);
Being $name, the name of the collaborator.
I hope this helps to those people that still use ZF1.
Greetings,