Please be careful using that word. It should not be used lightly. The MBS are munafiq not k*ffirs.
I think a munafiq is necessarily a kaffir. I believe a munafiq by definition is a kaffir who poses as a Muslim. I think calling someone a munafiq is thus a form of takfir. A muslim can have elements of nifaq, they may have a limited amount of nifaq... but someone who is a munafiq I believe is necessarily a kaffir.