Such deception should lead to prosecution..Sexual status should be disclosed, anyway hope OP doesn’t feel too disappointed 
Unfortunately it’s a slippery slope. It would probably be hard to prove in court whether or not one was deceived into having sex with a post-op.
For example, if you have HIV and knowingly expose someone to the disease maliciously, you still have to prove the intent was there and the sexual victim wasn’t aware of your status. Plus, using protection absolves that person of any legal ramifications. Now actually passing it on is a more concrete grounds for prosecution.
I doubt that we will ever see any laws passed where post-ops will have to disclose their previous gender. No government would want to be seen as transphobic, especially with how powerful the LGBT community is. We just have to do our due diligence as punters to avoid these situations.