1. Replace newlines to XX: :%s/\n/XX/
   • Replace the above % with a range to apply the replacements only to a specific range
2. Replace XX with newlines: :%s/XX/\r/
   • Replace the above % with a range to apply the replacements only to a specific range
   • Note the use of \r instead of \n this time

Reference:

• https://www.linuxquestions.org/questions/linux-newbie-8/vim-remove-line-breaks-757993/