Paul state after his conversion that he is still Pharisee on two occasions
Now when Paul perceived that one part were Sadducees and the other
Pharisees, he cried out in the council, “Brothers, I am a Pharisee, a
son of Pharisees. It is with respect to the hope and the resurrection
of the dead that I am on trial.”
circumcised on the eighth day, of the people of Israel, of the tribe
of Benjamin, a Hebrew of Hebrews; as to the law, a Pharisee;
Near the end of his life he also stated
After three days he called together the local leaders of the Jews, and
when they had gathered, he said to them, “Brothers, though I had done
nothing against our people or the customs of our fathers, yet I was
delivered as a prisoner from Jerusalem into the hands of the Romans.
So we clearly see Paul/Saul staid pharisee his whole life , so it is possible.
I think it is later on jewish leaders made some complications for christian and jewish believers in Jesus Christ to worship in synagogue(e.g Eighteen Benediction). After jewish brothers felt betrayed by jewish believers in Jesus when they run away from the country and didnt fight the romans