Snippets: newlines

Text:
11111
222
(Empty line)
4444444(EOF)

Goal:
11111
11111
222
222
(Empty line)
4444444
4444444(EOF)

So I made a snippet “Duplicate Lines Interlaced” (1):
${0:${SelText/.+(\r?\n|\r)/\0\0/g}}
▲?1: Have to use \r and/or \n exactly. Can this be simplified in Snippets?
▲?2: Newlines are consistent in the result. Is it possible to keep the original?
▲?2+: Note that the length of the selection in the result could be shorter or longer than expected, if the original newlines are inconsistent.
▲?3: This snippet can not handle the EOF line. How to handle EOF in Snippets?

Snippet “Duplicate Lines Interlaced” (2):
${0:${SelText/.+/\0\n\0/g}}
▲ This one can handle the EOF line. But apparently the newline issues still exist.