Would somebody be so kind and told me how to create the "rdr" rule for 
the firewall (using exec.php)?

I need to do something like this:
Source IP/mask proto TCP/udp ->to Desination IP proto(TCP/UDP):port 
-> REDIRECT to Desination IP:PORT 

I suppose it is possible to take "rdr" or "forward" directives in this 
purpose, however I don't know how, not even how to put rule in to  
m0n0wall.
I found quite a lot of posts referring this problem, without none exactly 
replies. 
Manuel why you didn't put the rdr rule for the configuration of the 
firewall so far?
It is possible to use it, for creating transparent proxy on the external 
machine, for the traffic optimization or also content filtering (external 
machine too).
KS