Use of が

Hello. So imre-reading through the early chapters of my Genki text book and decided to think a bit more about the usage of が。Namely, one of the first sentences it is introducing is 私の専攻は____です。 So I'm wondering, would it be appropriate to also do 私は専攻が? If I were to guess, it would be like the conversation is about myself, and the current statement is my major, rather the the subject of the conversation being my major.

That structure is called はが文. は indicates the subject, and the rest, for instance, 専攻が化学です is an explanation about the subject. There is another version in this structure, e.g., 学生は勉強が本分です. In this case, it can be rephrased to 学生の本分は勉強です, not 学生の勉強は本分です.