Are you not able to consider that the Dead Sea scrolls were copied incorrectly ie with the copiest's ideas about what it should say?The idea of "changing" the Bible to conform to our ideas of moral rightness shows a fundamental misconception about what the Bible is.
The Bible isn't a how to guide on morality so much as it is a record of testimonies. When someone gives their testimony regarded events that occurred or things that were said, it isn't considered proper to go and change the testimony because you disagree. The idea of say going into the book of Mark and changing it to say something else that fits how we think it should be is strange because then it wouldn't be Mark's testimony anymore - it would be our own corruption of it.
The reasonable way to consider changing the Bible is to consider if there are more accurate documents of the various Books of the Bible or to add new Books that are relevant. This sort of thing is a matter of historical research and the search for authenticity. This means looking at testimonies such as the apocrypha or examining the contents of the Dead Sea scrolls as they relate to existing testimonies to make sure those testimonies are as complete and authentic as possible.
This is why even if the testimonies are considered to be flawed, the idea of changing the Bible to conform to our own philosophies is an even more flawed notion. As the old adage goes: "two wrongs don't make a right".
Why might it be possible to add mistaken meaning now, but not possible when the scrolls were first copied?
The Dead Sea scrolls are copies. The first written documents do not exist anymore. Also, some of what was written wasn't actual testimony but was hearsay.