“Reverting” the auto-fill in emacs

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