Ethernet fake answer to a existing program with Borland C++

Question

Hello, I have a project, the following
I have a program that communicates with several modules (Moxa) ethernet to rs-485
each of these modules has an IP address and mac

What I would do is to receive packets sent by the program
to the network card and these modules and send a reply reception
(ARP) without these modules am present (a fake) The reason of
all this,

is to eliminate these module (moxa) and send all packets in a file
I would treat thereafter with another system

I want to know if this project is feasible

I have Borland C + + Builder

So I would sniff the network port, filter addresses (I already know the address and port)
and send a reply to the existing program reception, so he'll think
send it all and had a response of the modules.

A problem that I see is the calculation of the response (push ARP)

I want to know if this project is feasible

p.S I am French Canadian I use a translator for write