Reinjecting modified packets in netfilter module

I have used netfiler_queue to create a NFQUEUE module for iptables that handles all outgoing UDP packets.

I want to modify all UDP packets that match a certain pattern, and reinject them into the network.

Here is some example code:

...

static int Callback( nfq_q_handle *myQueue, struct nfgenmsg *msg, nfq_data *pkt, void *cbData) {
  uint32_t id = 0;
  nfqnl_msg_packet_hdr *header;

  if ((header = nfq_get_msg_packet_hdr(pkt))) {
    id = ntohl(header->packet_id);
  }

  // Get the packet payload
  unsigned char *pktData;
  int len = nfq_get_payload(pkt, &pktData);

  // The following is an example. 
  // In reality, it involves more parsing of the packet payload.
  if (len && pktData[40] == ') {
    // Modify byte 40
    pktData[40] = 'Y';
  }

  // Pass through the (modified) packet.
  return nfq_set_verdict(myQueue, id, NF_ACCEPT, 0, NULL);
}

...

int main(){

  ...

  struct nfq_handle nfqHandle;
  nfq_create_queue(nfqHandle,  0, &Callback, NULL)

  ...

  return 0;
}

I am not allowed to share the full source code, so this example is made specifically for this question, I hope this example code is not too dumbed down.

The modified packet does not get reinjected into the stream. How would I inject the modified version of the packet?