Update: davebaker changed this post (without citation!) while I was composing this reply.

---

... a data block or file that contains “old string”~“new string” lines:

__DATA__
... an email\x{0A}to ....~For more information, ....
(Is that what you mean?)

No. (Well, at least that's not the point I would make. :)

The point I would make is that the string you get | read from a __DATA__ or __END__ block or from a regular file is essentially the same as a single-quoted string defined in a script, and such a string can be used directly as a regex search pattern:

Win8 Strawberry 5.8.9.5 (32)  Tue 03/16/2021 17:26:59
C:\@Work\Perl\monks\davebaker
>perl -Mstrict -Mwarnings

my $s = 'foo
bar';
print "A: >>$s<< \n";

my $search  = 'foo\nbar';   # note single quotes!
print "B: >>$search<< \n";  # \n is '\n'

my $replace = "hoo-ray";  # can be single/double quotes

$s =~ s/$search/$replace/;  # no /g - one replacement only
print "C: >>$s<< \n";

^Z
A: >>foo
bar<<
B: >>foo\nbar<<
C: >>hoo-ray<<
[download]

If the search string/pattern is held in a file, the process is similar, except you usually need to chomp the string before you use it:

Win8 Strawberry 5.8.9.5 (32)  Tue 03/16/2021 17:28:26
C:\@Work\Perl\monks\davebaker
>type search.dat
foo\nbar

>perl -Mstrict -Mwarnings

my $s = 'foo
bar';
print "A: >>$s<< \n";

open my $fh, '<', 'search.dat' or die "opening: $!";

chomp(my $search = <$fh>);
print "B: >>$search<< \n";  # \n is essentially '\n'

my $replace = "hoo-ray";

$s =~ s/$search/$replace/;
print "C: >>$s<< \n";

^Z
A: >>foo
bar<<
B: >>foo\nbar<<
C: >>hoo-ray<<
[download]

I think that if you use '\n' (or the equivalent from a file) in a regex search pattern and if you use default I/O for reading all your files, then you will be able to do automatic text editing in an OS-agnostic way, at least across the Windows/*nix iron curtain. The '\n' sequence in a regex is the universal representation of a default newline.

(In general, I think use of qr// is definitely best practice for defining search regexes in a script, not single- or double-quoted strings, but if you're reading from a file, you're kinda stuck with what you've got.)