Can a FileVault-encrypted partition be accessed using a password I supplied during OS X install?
Once you change the password, it has been charged and the old password can not access the FileVault decryption protocol. It would be nightmarish if you had to always remember any and all passwords ever used by the FileVault account(s). 

If you want really great info to FileVault please watch: http://docs.macsysadmin.se/2013/video/Day2Session5.mp4