user1761: I'm playing with raw transactions. It's easy to send two signed valid transactions at the same time from the same output to different addresses (making a double-spend attack). My doubt is: if I make tests like this, will the bitcoin p2p network will flag my node / IP as "bad" or I can do it normally without any consequences? Of course I am not attacking anyone else, I want to make tests with my wallets / system to see the behavior.

user13413: No, spending an already spent output is not a DoS banning offense. Sending invalid transactions will however get you banned from your peers. 

user12983: Your current peers can ban (for some time, not forever) your IP-address.
Just connect to other nodes in case.
The network itself can not do anything with you because there is no such thing in protocol.
Your peers do not know - are you a double-spender or you just relaying somebody's else packets.
(Sorry, my English is also very poor)

1761: <p>I'm playing with raw transactions. It's easy to send two signed valid transactions at the same time from the same output to different addresses (making a double-spend attack). My doubt is: if I make tests like this, will the bitcoin p2p network will flag my node / IP as "bad" or I can do it normally without any consequences? Of course I am not attacking anyone else, I want to make tests with my wallets / system to see the behavior.</p>
 13413: <p>No, spending an already spent output is not a DoS banning offense. Sending invalid transactions will however get you banned from your peers. </p>
 12983: <p>Your current peers can ban (for some time, not forever) your IP-address.
Just connect to other nodes in case.
The network itself can not do anything with you because there is no such thing in protocol.
Your peers do not know - are you a double-spender or you just relaying somebody's else packets.</p>

<p>(Sorry, my English is also very poor)</p>
