char nick[] = "yourNewName";
strcpy(playerInfo[g_myPlayerID].szPlayerName, nick);
RakNet::BitStream bsSend;
char auth_bs[4*16] = {0};
pSamp->getSerial(auth_bs);
BYTE byteAuthBSLen = (BYTE)strlen(auth_bs);
BYTE byteMod = 1;
BYTE byteNameLen = (BYTE)strlen(nick);
unsigned int uiClientChallengeResponse = settings.uiChallange ^ iVersion;
bsSend.Write(NETGAME_VERSION);
bsSend.Write(byteMod);
bsSend.Write(byteNameLen);
bsSend.Write(nick, byteNameLen);
bsSend.Write(uiClientChallengeResponse);
bsSend.Write(byteAuthBSLen);
bsSend.Write(auth_bs, byteAuthBSLen);
pRakClient->RPC(&RPC_ClientJoin, &bsSend, HIGH_PRIORITY, RELIABLE, 0, FALSE, UNASSIGNED_NETWORK_ID, NULL);