To delete blank lines, I would bookmark all regular expressions:
^$
(use “Bookmark All” button in the Find dialog box)
and then use the Delete Bookmarked Lines command.
If you have enough physical memory in your PC, and if you need to replace many multi-line text (combine lines or split lines), you might want to try clearing the Use Temporary File to Reduce Memory Usage check box in the Advanced tab of the Customize dialog box.
Thanks,