None of the suggestions found here work, nor does a search on issues in the repo turn up anything.
I'd like to replace all >< with >\r\n< inside a selection 
'<,'>s/></?/g
what goes in place of the question mark?
Does this work for you?
:'<,'>s/></>\r</g
Are you on windows and trying to insert both (literal) \r (carriage return) and \n (new line) ?
 
    
    I just had success a moment ago moving asterisks to the start of a new line (i.e. replace asterisk chars with newline + asterisk) with:
:%s/\*/\r*/g
for clarity, that's:
:%s   (replace in whole file)
\*    (literal asterisk)
\r*   (new line followed by literal asterisk)
g     (operate on all matches on any given line)
