Any person at any time can reject their salvation. There is a very, very, huge difference between sinning and the conscious act of rejecting the salvation of Jesus Christ by literally saying that there is no GOD or Christ. That is where the heart becomes so hardened toward GOD the person with full understanding rejects it. IF you are in this state when you die there is no salvation. If an event in your life brought you too this point in anger or hurt and you repent and ask forgiveness that is another matter also as I believe it can be forgiven. Yes GOD understands. The rejection of Christ is also not Preacher Jones who for his life served GOD is laying in a Dementia unit cursing GOD. Preacher Jones knows not what he does.
GOD gives us free will. Hitler made his own choice. Either the seed of salvation was planted in him and he let it deliberately die even after The Holy Spirits attempt to teach him or he never in earnest asked for it to start with. Only GOD knows the truth.
Sin is a conscious choice; to know what is wrong and to choose to do it. It is abuse of the freedom that God gave us; a rejection of Good and with it Salvation."
..."the conscious act of rejecting the salvation of Jesus Christ by literally saying that there is no GOD or Christ"
There is no specific incantation to reject Salvation, but there are conscious choices that negate it and regain it No one is completely cut of from Salvation, nor confident of it until the moment of their death. Your admission is that "Always" doesn't always mean always, though.