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");