Hello!
It can be only one engineering device in the project.
You may add several non-engineering devices into the project to hi-lite it’s ip addr. Please take a look at embedded manual page
Can you tell what configuration settings of plc will be changed from unit to unit? If you have to modify just ip addresses, it will be more wise to use Ad-hoc IP substitution in base project.
The way of connection of several plc’s also will be depends on your common requirements. But Profinet will provide more robust time of data exchange, also there will be less code for manage client and server connection.
Modbus TCP will make you able freely organize data exchange with third party devices.
BR