Renaming the farm with it's original name demonstrates that the transformation the farm underwent came full circle.
It started with a terrible master who cared very little for his animals and it ends with a terrible leader who willingly sacrificed the lives of his animals for his gain. This resembles what happened during the Russian Revolution as Stalin's dictator-like leadership and carelessness for human life mirrored that of the previously ruling Romanovs.
I guess you could say he renames Animal Farm. But actually what he does is just goes back to using its original name. So I don't know if that counts as renaming it. Anyway, what he starts to call it in this toast is the name it used to have -- Manor Farm.
When Napoleon does this, he shows that he has really come all the way to being just like Jones. He walks on two feet, drinks alcohol, hangs out with people, and now he brings back the original name of the farm.