Some of the core teachings held by Jehovah's witnesses are: no hell, no trinity, no saints to worship, no virgin marry, resurrection on earth, no learned prayers.
The problem here however is that these are not really core teachings. If they had been, Jesus would have spent much more time to elaborate on these. Rather, he spent much of his time denouncing hypocrisy, liars, tyranny, those who judge, the type of core teaching that is actually understood by the great majority of christian religions.
What has changed through the years? Things that actually change the lives or the christian and deal with the core teachings of christianity: No blood, preaching work as a requirement, no smooking, no celebration of the majority of holidays, no beards, disfellowshipping, understanding of apostacy, demogracy in the congregation, acceptance of civil service vs going to war, etc.
It is not because you change something that you can call it details. These things all change the way JW live their lives and puts boundaries on how and where they display love.