Convert bin model to pickle
Pickle is not a format but a protocol to serialize a python object to binary format.
In the documentation of gensim, you can read they actually use pickle for serializing to binary format.
You can of course use pickle library instead of the .save method in gensim, but it will be exactly the same, since gensim already use pickle. I would recommend you to use .save method however, because gensim likely has better way to handle the hierarchical structure and dependencies of your model.