No, there is no option to go back.
And asking on different Forums will not get you an different answer.
It says, when you start Knights of the Fallen Empire, that you will not be able to go back and do other stories. It asks you three times to confirm that you want to start Knights of the Fallen Empire, and at least 2 of those times mentions that you can't go back.
They can't really make it any more clear that you can't go back, you have to meet them halfway by at least reading things before you click confirm the first time around. And it does include Shadows of Revan, but you have to do that content first, should have been a mission on your ship terminal to do so, Shadows of Revan starts with Forged Alliances.
