Hi,
1. I've already told you in my previous post:
You can do that thanks to the "shipping methods" restriction setting of your payment methods.
So I'm not sure what more you want me to tell you ?
2. That "free shipping" text is only used for shipping methods of course. So if you replace it, it will only affect the shipping method selection interface. You can search for tha translation string FREE_SHIPPING throughout the code of HikaShop, and you'll see that it's only present in the file "shipping" of the "checkout" view.