As a form of payment, if you were accepting SECI via SeciPay on your eCommerce website, no you wouldn't alter the SECI core code to do that. SeciPay is essentially a payment gateway, like Authorize.net or Paypal, for crypto.

You could fork SECI into your own coin/blockchain, if you like, because we are open source. Or, you could fork SeciPay, because it is also open source, but if you are simply using our products/services, you can't alter the code and it still be SECI.

If you were to use the still-under-design-and-development SECI Blockchain Solutions side-chain for a business application, etc, you wouldn't be "accepting it as a form of payment", you would pay SECI as a toll to utilize a side chain to run an application/service/etc. In that case, there will be some options for your side chain (TBD), but no you would not be altering the fundamental code of SECI itself. Your app would do whatever it was designed to, and use the SECI side chain for public or private confirmations, etc. You wouldn't be building your own blockchain as a side chain to SECI, the side chain is provided for you to integrate with.