Is it permissible to say, "If I were a man, I would be a mujahid (one who strives in the path of God)," and "If I were a man, I would be praying in the mosque," out of intense love for these deeds and not as an objection to divine decree or a belief in altering destiny?

You must be wary of obsessive whispering (waswasah) and strive against your soul to rid yourself of it. The belief that causes change destiny is incorrect. Allah predetermined and knew all things eternally, and His knowledge does not change. However, He decreed that things occur through causes. If a servant does not perform a deed, what is written will not change. Allah alone knows what was, what is to be, and what would have been if it had been. This is like wishing for jihad if one were a man, and similar thoughts for which a woman is not sinful, as she has other fields for jihad.