Within Tibetan Buddhism, are the Lamas always the same "soul"? It's my understanding that the belief in Tibetan Buddhism is that when a Lama is reborn he (not meaning to be sexist, but I know of no female Lamas - please let me know if I'm wrong) becomes that same Lama again.  From a western viewpoint, it might be said his soul is put into a new body and he returns as the same Lama in the new body.

However, recent comments by the  Dalai Lama have me wondering about this.  It seems he wants to be reborn in order to continue helping others, but without becoming the Dalai Lama again.  (It has been speculated that there may be political motivation to this, as the Chinese want to designate the next Dalai Lama.)  However, wouldn't the 14th Dalai Lama become the 15th Dalai Lama if he is reborn?  Would a Lama be able to end a series of Lamas even though he is reborn? (I have heard of Lama lines ending, but it's my understanding that the belief is that the Lama chose not to reborn.)

Or is my understanding here completed off base?
Because Buddhism denies the notion of "self", it does not have a concept of Avatar, as someone literally being a reincarnation of the same "self".

Tibetan Buddhism does have a notion of Tulku though, which is similar. Tulku is a new person that inherits the life stories and experiences of a previous person. This is done through teaching this person to deliberately identify with their predecessor, to learn predecessor's history, and to carry on his or her work.

Because the new person's life is so heavily influenced and inspired by the predecessor, we can say that the new person is an embodiment of the abstract energy of the previous one.

The case with your specific question, any person, and even multiple people, regardless of status or title or role, could be designated as Tulkus of Dalai Lama, but to truly qualify as such, the person would need to seriously work on their identity as an embodiment of Dalai Lama's heritage.