Hello Ankit,
For C4C to ECC flows - Unfortunately there is no other way where you can configure standard flows to connect to multiple ERP Systems or clients, than editing the standard Interfaces from SAP. Do note that certain iFlows that have been determine as configure only would need to be re-created from the scratch.
For ECC to C4C flows - this is rather easy as the SM59 destination in ECC will need to point to the same iFlow URL and that is about it. The challenge though here will be when the data goes to C4C - how will C4C know which Client this data from etc.
Regards,
Bhavesh