Enter \n\n in the “Search for: box, and ~!~ in the “Replace with” box, then click on the Replace All button. That replaces all the double line feeds with the string “~!~”. I’m doing this because I’ll replace single occurrences of \n with a space. If my first find-and-replace was for the single occurrences of \n, paragraphs would run into each other.

The Search-and-replace dialog box stays on-screen. Now, Enter ~!~ in the “Search for” box, and \n\n in the “Replace with” box, then click on the Replace All button. That one breaks paragraphs with two line feeds.

If you prefer to keep Regular Expressions disabled, uncheck the relevant check box. Close the Find-Replace dialog box, stop the macro recording.

One thing I haven’t checked is the effect of paragraph styles on the macro. Like, in my default style sheets, I have two line feed between paragraphs. If that’s also the case for your default style sheet, your replacement string for ~!~ will be a single \n.

As to the ~!~ thingy, I chose that on the assumption that text normally wouldn’t contain that character. Might be safer to use a longer string, e.g., ThisStringIsTemporaryParagraphBreak — since this is a macro, you’ll be doing that only once anyway :)