GTM Global sync group help

The answer to your question lies within. In regards to the first question... No. In regards to the second question. Any zones you create are automatically replicated across GTM's. How you choose to structure resilution is entirely up to you as long as it follows correct DNS behaviour. It usually comes down to an administrative choice rather than a GTM one. In any case before you go down a path which changes the DNS domains I suggest you run it up on a test platform it to make sure it works as you expect. Eg GTM understands it. The information you have provided here is not enough to say one way or the other. Provide actual before and after DNS examples (sanitized) and then we will have a better idea of what DNS changes you propose and we can comment further.