Here's one way to do it with a regexp: 

# cat 1139933.dat
para1 foo bar
para1 some stuff

para2 other stuff
para2 foo bar

para2 extra stuff

para3 this is enough
#

[download]

# perl -Mstrict -wne'
  $/ = ""; s/^(para2.*)^$/$1new text\n/ms; print;
' 1139933.dat
para1 foo bar
para1 some stuff

para2 other stuff
para2 foo bar
new text

para2 extra stuff
new text

para3 this is enough
#

[download]

Update: new solution; hippo beat me to my first idea

The way forward always starts with a minimal test.

In reply to Re: one liner append line(s) to matched paragraph by 1nickt
in thread one liner append line(s) to matched paragraph by PeteInPDX

Title:
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