Agree with the comments above re. finding a better reroute, but if you do ultimately travel WTP then check-in should be able to issue you a manual boarding pass showing that you are eligible for lounge access. I have had this done before.

I suspect you would be allowed into the FW by showing your original booking and the downgraded BP, and clearly if you are going through FW security you will end up in the First lounge. I'm not sure if someone might be willing to mention the CCR expressly.