Win8 Strawberry 5.8.9.5 (32)  Fri 11/06/2020 19:28:21
C:\@Work\Perl\monks
>perl
use strict;
use warnings;

my $string = 'foo + bar == baz';

my %xlate = (
    'foo' => 'wibble',
    'bar' => 'wobble',
    'baz' => 'boff',
    '+'   => 'plus',
    '=='  => 'equals',
    );

my ($rx_token) =
    map  qr{ $_ }xms,
    join ' | ',
    map  quotemeta,
    reverse sort
    keys %xlate
    ;
print "\$rx_token $rx_token \n";  # for debug

print "before: '$string' \n";

$string =~ s{ ($rx_token) }{$xlate{$1}}xmsg;

print "after:  '$string' \n";

^Z
$rx_token (?msx-i: foo | baz | bar | \=\= | \+ )
before: 'foo + bar == baz'
after:  'wibble plus wobble equals boff'