$ cat with_utf8.pl 
use warnings;
use strict;
use utf8;
use Devel::Peek;
my $string = 'Fräsen und ndk (Kamera - Fräsaufnahme)';
Dump($string);

$ perl -pe 's/^(?=.*utf8)/#/' with_utf8.pl | tee without_utf8.pl
use warnings;
use strict;
#use utf8;
use Devel::Peek;
my $string = 'Fräsen und ndk (Kamera - Fräsaufnahme)';
Dump($string);

$ iconv -f UTF-8 -t Latin1 without_utf8.pl -o latin1.pl
$ file -i *.pl
latin1.pl:       text/plain; charset=iso-8859-1
without_utf8.pl: text/plain; charset=utf-8
with_utf8.pl:    text/plain; charset=utf-8

$ perl latin1.pl 
SV = PV(0x1365d70) at 0x13855c0
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0x13d7160 "Fr\344sen und ndk (Kamera - Fr\344saufnahme)"\0
  CUR = 38
  LEN = 40
  COW_REFCNT = 1

$ perl without_utf8.pl 
SV = PV(0xa15d70) at 0xa355c0
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0xa87190 "Fr\303\244sen und ndk (Kamera - Fr\303\244saufnahme)"\0
  CUR = 40
  LEN = 42
  COW_REFCNT = 1

$ perl with_utf8.pl 
SV = PV(0x18d5d70) at 0x18f55d8
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK,UTF8)
  PV = 0x19384a0 "Fr\303\244sen und ndk (Kamera - Fr\303\244saufnahme)"\0 [UTF8 "Fr\x{e4}sen und ndk (Kamera - Fr\x{e4}saufnahme)"]
  CUR = 40
  LEN = 42
  COW_REFCNT = 1