data
-------------------------
para1 foo bar
para1 some stuff

para2 other stuff
para2 foo bar

para3 this is enough
-------------------------

if paragraph's lines start with para2, then append
new line(s) to that paragraph

desired
-------------------------
para1 foo bar
para1 some stuff

para2 other stuff
para2 foo bar
para2 NEW STUFF

para3 this is enough
-------------------------

going nuts with trying to set -F to \n\n or using -00