Is this possible?
A: You should be able to write a Modbus client in any language that has access to the serial ports or a TCP connection.
C# has access to both the serial port and a RAW TCP connection; it will not be too hard to create a simple Modbus Client with C#.
I have to ask, Why would you want to create a anther Modbus Slave utility when there are already so many good freely available ones out there?
I would recommended that you take a look at CAS Modbus Scanner, it’s a free Modbus client that you can use to test your Modbus devices