No need to add anything to scripture. But where do you get the idea that God was talking about "spiritual" death? If we're referring to Genesis, that concept isn't needed or explicit, so why would you feel the need to add it?
He defined exactly what He meant by death:
[
Gen 3:19 KJV] In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken:
for dust thou [art], and unto dust shalt thou return.
In Genesis 2, God points out how Adam would die...if he ate of the fruit. The reverse corollary is that he would not die if he didn't eat. Maybe that's not true, but then we see that Adam had access to the other tree. If access to the tree of life would result in immortality after the fall, why would it do less before the fall? The very information you provide that says Adam "could become" immortal after the fall is the very information already provided that he could have been immortal before.
Obviously we aren't talking about a man who
cannot die, because eating from the tree of knowledge would cause him to die, according to God, but we are talking about a man who
would not die...unless he ate. Growing old wouldn't bring death. Just sin.
[
Rom 5:12 KJV] Wherefore, as by one man sin entered into the world, and death by sin; and
so death passed upon all men, for that all have sinned:
Does that verse make any sense if death was the end result of life before sin entered the world?
