On my Windows 7 computer, I had to do it a little bit different; there were two files to change.
Under the Documents\My Games\FallenEnchantress\Units folder, I edited the file named after my custom sovereign. I moved my original back story (which had been saved but didn't show up in game) from <BackStory>...</BackStory> to <LorebookIntroText>...</LorebookIntroText> (having to create the latter <> entry as parrottmath suggested). Instead, you could probably just twice change "BackStory" to "LorebookIntroText," but I didn't try that.
Under Documents\My Games\FallenEnchantress\Race folder, I edited the file named after my custom faction. I edited the text between <Description>...</Description>.
Everything now shows up where it's supposed to.