Is it possible to reset FileVault password in recovery mode?
If you have the recovery key (assuming it's the alphanumeric kind), you can reset your account password in the following way:


Boot your Mac to the FileVault 2 login window.
Enter your password incorrectly three times
It should prompt you for your recovery key. Enter it and hit return.


Your Mac should boot and stop at the OS's login window.


When prompted, reset your account's password.


If your Mac isn't able to boot from its regular boot drive and you can only start from the recovery drive, you should unlock and then decrypt your Mac prior to trying to fix your Mac. I have a post available here showing how to unlock and decrypt your Mac using your recovery key:

Unlock or decrypt your FileVault 2-encrypted boot drive from the command line