How many process code we can assign into a message type and idoc type

Hi Experts,

I have a requirement in idoc, we have existing partner's sender and receiver. But our client wants from our outbound setup will same but in inbound setup just add one more partner.so we are copied inbound part from exist partner and changed that partner number.but we need to change that function module inside the process code for as per our client requirement.If we are changing function module in our new partner the changes effecting old partner also because process code is same.

So i have one doubt if we create a new process code and assign to that messages type how system will behave. it can capture both process code or it can only one.or we need to create both message type and idoc type.

Anyone can help me for this requirement.

Thanks,