[Perkin]

One way I do a similar thing is with a bulk s&r (minimal match, regex and match case).
Search for

</p>(.)(.)  <p>([a-z])

the (.) get the newlines, and there's two spaces (for the indentation - you may need more if you <p>'s are inside <div>'s

Replace with

 \3

note there's a space preceding the slash

This will re-flow the lines that begin with lower case letters only.

Edit: spelling