I wonder if there is a more elegant solution to this. I guess it could be wrapped up into a neat function that works on every paragraph marked/selected.
Most of the time I use emacs with auto-fill mode breaking any line at 70. Sometimes though I’d like a paragraph to be reverted to a single line; for example for copy-pasting into other editors where it could breaks the formatting. Here’s how
M-x set-variable RET fill-column RET 100000 M-q (on the desired paragraphs) M-x set-variable RET fill-column RET 70
First line set the fill-column to a large amount, the second will re-run the fill-paragraph and the third will reset the fill-column to my usual value