Hello Iswari,
Data would be sent from ECC to CRM, which has been registered in ECC table CRMRFCPAR.
So just changing RFC connection details in SM59 will not help, in changing the destination to which data has to be sent.
There are options to connect multiple CRMs to single ECC, provided underlying business object support this MCRM scenario.
Or you can explore other way of data exchange which do not include CRM Middleware, so that existing data exchange set up do not get disturbed.
Best Regards,
Shanthala.