Q. When Adam added to God’s command in the Garden of Eden and told Eve that God had said not to touch the tree, rather than just not to eat of its fruit, was that a lie? How did that happen before sin entered in the world?
I will address your specific question shortly, but I should note first that Adam did not necessarily add to God’s command.
As we read through the Genesis creation account, we see that God gave Adam the command about the Tree of the Knowledge of Good and Evil before he created Eve. God’s command was simply not to eat of the fruit of the tree, but Eve told the serpent, “God said, ‘You must not eat from it, and you must not touch it, lest you die.'” One possible inference is that Adam told Eve that God had said this. However, there are some other possible explanations.
For one thing, Eve could have been using the word “touch” in a poetic sense to mean “have to do with.” In that case she would be repeating God’s statement for emphasis, and while she would not be quoting it literally, she would be conveying its meaning accurately: “You must not eat from it, indeed, you must have nothing to do with it, lest you die.”
Another possibility is that Adam and Eve agreed together that the best way to keep from eating the fruit of the tree was not even to touch it. Eve would then be mentioning not touching the tree as a natural outgrowth of the command not to eat from its fruit. Once again,she would not be quoting God literally, but she would be conveying the sense of the command as she and Adam had decided to obey it.
But it is admittedly possible that Adam himself added the stipulation not to touch the tree when he communicated God’s command to Eve, knowing that God had not said this, but leading Eve to believe that God had indeed said it. This would not have been, strictly speaking, a lie, since a lie is an intentional misrepresentation of the truth whose motive is to gain personal advantage or to harm another person. If Adam added to the commandment, it was with the best of motives.
Still, the end does not justify the means. Even with a good motive, it would have been wrong for Adam to tell Eve that God had said something when God had not actually said it. It would have been better for Adam to trust Eve and to trust God’s work in her heart and not think that Eve had to be deceived into obeying God. So if Adam actually deceived her knowingly, I think we would have to consider that a sin.
So how could Adam have committed such a sin before he and Eve ate the fruit of the tree and “sin entered the world through one man,” as Paul says in Romans?
We might just as easily ask how Adam and Eve could have disobeyed God and eaten from the fruit of the tree before sin entered the world, since that disobedience was itself sin. The answer is that Adam and Eve were not under the power of sin before they disobeyed God, but nevertheless they had complete moral freedom, which meant that they were able to obey and also able to disobey.
If we believe that Adam added to God’s command and therefore made it harder to obey, we should see that as part of an entire sequence of actions that ultimately constituted disobedience. When someone does something wrong, is rarely possible to look at the whole sequence of their actions and say, “There—that specific point is where the sin occurred.”
So if Adam did add intentionally to God’s command, then that was part of an exercise of moral freedom that unfortunately ended in him and Eve disobeying God and bringing all of their descendants under the power of sin.
Good Question 
Thank you