You can send bytes if you wish, but typically you'll put more into the buffer before sending the datagram. Example you might write out op code byte, and then write integers for x,y,z.. then do SendUDPMsg.
WriteByte(udp_wr,byte1)
; send all characters in the stream buffer.
SendUDPMsg udp_wr,IP,Inp_Port
WriteByte(udp_wr,byte1)
; send all characters in the stream buffer.
SendUDPMsg udp_wr,IP,Inp_Port