In your case, I would say you do a back up from ZD1100, then restore it in ZD1200. When you restore it, click the option "just configuration, WLAN, access role...."
After it done, I would update ZD1200 to 9.10 firmware (just optional).
Then you can turn off your ZD1100, so your APs will connect to ZD1200.
Please make sure ZD1200 are same subnet with ZD1100.
One important thing is you need to make sure your ZD1200 have enough licences for your APs.
All the best.