How can I delete everything from XXXX to the last line before an empty line in a text document?

Given a text document with multiple instances of the content:

XXXX
random number of lines with random text
other random text
more random text
random text
'blank line'

i want to delete everything between XXXX and the random text in the line before the blank line, and insert a comma before the random text so it looks like this:

XXXX,random text
'blank line'

How can I do this with a single command?

I currently use sublime text 3 and notepad++ on windows 10 but this question is platform agnostic. I'll use anything that works, thanks!

Assuming that "things" and "stuff" are always the same, you could use this:

Find what: XXXX\r\nthings\r\nstuff.*?\r\n(.*?)\r\n\r\n
Replace with: XXXX, \1\r\n\r\n

Where:

• \r\n\ : stands for the Windows end-line (carriage-return, line-feed)
• .*? : 0 or more character, non-greedy search
• () : defines a group
• \1 : the contents of the matched group.

Here is my test-case:

And here is the result after clicking Replace All:

With Notepad:

• Find what: XXXX\K\R(^[^'].+$\R){1,}
• Replace with: \r\n
• Search mode: Regular Expression

Before

After