This mod allows you to edit a book text in your favorite book editor and preview your changes in-game. After you are done, you can just copy-paste the text from the text file straight into your book's text field in the Construction Set! The mod allows you to preview the text in the book or the scroll menu. By default, the Alt-O combination will open a book menu, and Alt-P will open a scroll menu. The book text is loaded from a file: "Data files\booktext.txt". Write and save your changes to the file, then Alt-tab back into Morrowind and press Alt-O. Now you'll see the results of your changes. For the scroll, the text is loaded from: "Data files\scrolltext.txt".
In addition, you can change some settings in the MCM. You can make the mod add a book that loads its text from the mentioned text file to your character's inventory. This is an alternative if you don't like the hotkey way. The mod can automatically add the book if it detects that your character doesn't have one copy of the book in their inventory, or you can add the book directly by using a button in the MCM. The same goes for the Preview scroll.
You can obtain the mod on its Nexusmods page.