Com o GNU awk
gawk -v RS="" '
match($0, /Identifier "([^"]+)/, m) {
print > (m[1]".txt")
close(m[1]".txt")
}
' sample.txt
Com Perl, usando o módulo Path :: Tiny de conveniência do CPAN
perl -MPath::Tiny -00 -ne '/Identifier "(.+?)"/ and path("$1.txt")->spew($_)' sample.txt