NEED INFO ON BLUE SHIELD COVERAGE!!!!
There are hundreds of different BCBS plans - yours will be unique to you and your employer who decides what coverages it will include. If it covered your arm lift then there's a good chance it could cover part of the thigh lift (that's a super-generous policy by the way!).
The people who will know for sure is your insurance company. Call the customer service number on the back of your membership card and they can tell you exactly if your plans covers this or not and under what cir****tances.
The best anyone on here can do is tell you what their plan covers and it's not likely to be the same state/group/employer as yours. My BCBS plan in Nebraska at a local hospital covers absolutely zero for all cosmetic procedures.