emacs/replace-with-newline
replace a character with a newline in Emacs
M-x replace-string RET ; RET C-q C-j.
C-q for quoted-insert,
C-j is a newline.
How to put a newline into the minibuffer
C-o
C-q C-j
C-q 12 (12 is the octal value of newline)
C-x o to the main window, kill a newline with C-k, then C-x o back to the minibuffer, yank it with C-y