If your welding disturbs the coating and leaves gaps or cracks in the stainless coating, it will allow air and moisture to contact and corrode the carbon steel

If your welding disturbs the coating and leaves gaps or cracks in the stainless coating, it will allow air and moisture to contact and corrode the carbon steel core. And once the core corrodes, the stainless coating becomes the weight bearing part, and you have a massive problem. Assembling this would presumably require some care and expertise beyond normal rebar.