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

my $result = '';
while (not $string =~ m/\G\z/gc) {
    if ($string =~ /\G([^\\*?]+)/gc) { # normal chars
        $result .= $1;
    }
    elsif ($string =~ /\G\\(.)/gc) {   # escaped
        $result .= $1;
    }
    elsif ($string =~ /\G\*/gc) {      # unescaped *
        $result .= '?';
    }
    elsif ($string =~ /\G\?/gc) {      # unescaped ?
        $result .= '#';
    }
}
$string = $result; 
print $string;     # prints 't#e\xt\? with escapes*'