...
s{([^\0-\177])}{N_escape($1)}eg;
...
sub N_escape {
    my $n = charnames::viacode(ord($_[0]));
    return defined($n) ? "\\N{$n}" : sprintf('\x{%x}', ord($_[0]));
}
...

#!/usr/bin/perl
use strict;
use warnings;
use charnames ();
use Encode qw(encode decode_utf8);
use Unicode::Normalize;

our $s1 = "\x55\xcc\x88bel \xc3\x9cbel gro\xc3\x9fe";
print STDERR "string: $s1 (" . &my_print($s1) . ")\n\n"; 

my $s2 = decode_utf8($s1);
print STDERR "decode_utf8: $s2 (" . &my_print($s2) . ")\n\n"; 

my $s2b = encode("iso-8859-1", decode_utf8($s1));
print STDERR "ISO-8859-1: $s2b (" . &my_print($s2b) . ")\n\n"; 

my $s3 = NFC($s2);
print STDERR "NFC: $s3 (" . &my_print($s3) . ")\n\n"; 

my $s4 = $s3;
$s4 =~ s{([^\0-\177])}{N_escape($1)}eg;
print STDERR "Unicode names: $s4 (...)\n\n"; 

exit;

sub N_escape {
    my $n = charnames::viacode(ord($_[0]));
    return defined($n) ? "\\N{$n}" : sprintf('\x{%x}', ord($_[0]));
}

sub my_print {
    my $string = $_[0];
    my $newstring = '';
    my @chars = split(//, $string ) ;
    for my $char (@chars) {
        $newstring .= sprintf('\x{%x}', ord($char))
    }
    return $newstring 
    
}

string: Übel Übel große (\x{55}\x{cc}\x{88}\x{62}\x{65}\x{6c}\x{20}\x{c3}\x{9c}\x{62}\x{65}\x{6c}\x{20}\x{67}\x{72}\x{6f}\x{c3}\x{9f}\x{65})

Wide character in print at C:\projekte\perl\unicode\uni_test5.pl line 12.
decode_utf8: Übel Übel große (\x{55}\x{308}\x{62}\x{65}\x{6c}\x{20}\x{dc}\x{62}\x{65}\x{6c}\x{20}\x{67}\x{72}\x{6f}\x{df}\x{65})

ISO-8859-1: U?bel Übel große (\x{55}\x{3f}\x{62}\x{65}\x{6c}\x{20}\x{dc}\x{62}\x{65}\x{6c}\x{20}\x{67}\x{72}\x{6f}\x{df}\x{65})

NFC: Übel Übel große (\x{dc}\x{62}\x{65}\x{6c}\x{20}\x{dc}\x{62}\x{65}\x{6c}\x{20}\x{67}\x{72}\x{6f}\x{df}\x{65})

Unicode names: \N{LATIN CAPITAL LETTER U WITH DIAERESIS}bel \N{LATIN CAPITAL LETTER U WITH DIAERESIS}bel gro\N{LATIN SMALL LETTER SHARP S}e (...)