I think the Bible--and the Church Fathers for that matter--often speaks in seemingly absolute terms, but that such texts are only speaking in such a way for emphasis (a rhetorical device), and are not meant to be taken in a woodenly literal way. When verses like this come up, I usually point out other passages that, if interpreted in as literal a way as Jn. 3:16 is sometimes interpreted, wouldn't make sense. For instance, the Bible clearly says that "those who acknowledge Jesus with their lips... will be saved". Well then, are mutes eternally damned? In answer to how one may inherit eternal life, Jesus first lists some of the 10 commandments (and gives a summary statement for some of them). After this he proceeds to instruct someone to sell all that they have and give the money to the poor. Does this mean that we must all obey the 10 commandments fully, and also sell all that we have and give the money to the poor? James asks "Can faith alone save?" and his obvious answer is in the negative. Does that mean that we should discount bedside conversions the moment before death since they had not way to "demonstrate their faith by their works"? Jesus said "be ye perfect even as the heavenly Father is perfect". Obviously we can't be perfect just like God, but can only approach his perfection via His uncreated grace, being a partaker of the divine nature.
We find the same types of things in the Fathers, and even in the liturgy. We say in St. John Chrysostom's liturgy: "holy things are for the holy," and then a moment later "one is Holy, one is Lord, Jesus Christ"; so, we need to be careful about taking things woodenly literally, and we need to remember that sometimes what a text says at face value, even if it sounds final or absolute, is not in fact final or absolute. A few other examples can be seen in how the Fathers speak of salvation. Some Fathers have said that "without toil, there is no salvation," others that "without fasting, one can hardly be a Christian," and so on. These statements can't be taken as absolutely as they are being stated.
So, 1) even when this verse is translated in a more absolute way, I don't believe it is consistent (with the rest of scripture or tradition) to interpret it in an absolute way; and 2) the verse should be translated, IMO, as closely following the MSS being used as possible, and words shouldn't be added to "make the passage more clear". The Church's teaching is clear enough, we shouldn't tamper with the Bible. Now, on the other hand, if there are MSS that justify a certain rendering, then there's certainly nothing wrong with choosing the rendering that you believe most faithfully represents the truth being expressed by the author of the passage. There are many many variants readings for the NT text, and not just unimportant ones (there were crucial theological arguments about which variant to use a thousand years ago, things are no different today). I hope I didn't delve too much into things not asked in this post.