All expensive time of day. It is necessary to implement the substitution of packages on the fly. In the packet, you need to invalidate the specified 2 bytes at the fixed address 0x43: 45. Random values are generated in each packet. 
My option is not correct, tell me in which direction to think / search.
if (tp.proto == TCP && tcp.dst == 502) { replace(tcp.data[0x43:45], 0x00)} 