my %conv = ( '*' => '?', '?' => '#' );
my $conv = quotemeta(join('', keys(%conv)));

my $string = 't?e\\\\xt\\\\* with escapes\\*';

my $result = $string;
for ($result) {
   s/(?<!\\)((?:\\{2})*)([$conv])/$1$conv{$2}/g;
   s/\\(.)/$1/sg;
}

print($result, "\n");

##</code><code>##

my $string = 't?e\\\\xt\\\\* with escapes\\*';

my $result = '';
for ($string) {
    /\G \\(.) /xgcs && do { $result .= $1;   redo; };
    /\G \*    /xgcs && do { $result .= '?';  redo; };
    /\G \?    /xgcs && do { $result .= '#';  redo; };
    /\G (.)   /xgcs && do { $result .= $1;   redo; };
}

print($result, "\n");

##</code><code>##

my $string = 't?e\\\\xt\\\\* with escapes\\*';

my $result = '';
for ($string) {
    $result .= $1 if /\G ([^\\*?]+) /xgcs;

    /\G \\(.) /xgcs && do { $result .= $1;   redo; };
    /\G \*    /xgcs && do { $result .= '?';  redo; };
    /\G \?    /xgcs && do { $result .= '#';  redo; };
}

print($result, "\n");