This should be in your plan. It's going to vary by what plan you have - you'll need the plan name and the group number associated in some cases. The insurance lady in your surgeon's office should know how to word the request to have it accepted. And you can always (and should) appeal if they say no the first time. Insurance companies almost always say no the first time.
My plan (also BCBS) doesn't have trans exclusions, so all transition related procedures fall under the surgical benefits. In-network coverage is 100% minus copays, deductibles, etc. Out-of-network coverage is 70% minus copays, deductibles, etc. Once you hit the out-of-pocket maximum, they cover the rest.
As an example, the surgeon doing my bottom surgery is out of network. I'm responsible for copays and deductibles, and any additional fees that don't exceed my out of pocket maximum. This amount includes what I'll pay in copays and deductibles. My out of pocket maximum for an out of network provider is $6k. So the most I will spend for medical treatment in a calendar year is $6k. After that, insurance pays 100%. That is why I am hoping to get as many stages in as possible before my insurance rolls over

When you talk to them, see what other things they cover. Many plans have travel benefits if you're having to travel for surgery, and some cover home health aides for post-op recovery.