Here is a patch to make the line spacing and justification settings selected from the reading settings (Aa) menu take effect in some epubs where they wouldn't work before.
It works by changing the built-in epub stylesheet so that the line spacing and justification settings are overridden at body and paragraph <p> level, instead of just body level. This is similar to what the kepub reader does.
Note: It still won't work on those books where the publisher has used <div> instead of <p> for paragraphs.
Also note: This is not the ideal way to get these settings to take effect, as it can result in some line spacing or justification settings in the book being overridden when they really shouldn't be. The only way to get perfect results is to edit the book and fix the problems at source.
See the note in the patch about commenting out a line if you are using the `ePub adjustable top/bottom margins` or `ePub fixed top/bottom margin` patches, as this patch changes the same part of the stylesheet used by those patches.