Hello Gowtham,
First of all, use a change management period for some downtime to do your switch over.
APs currently running under ZD code will not automatically connect to SZ, and vice versa.
You will need to update each of your 20 APs (lucky they have static IPs) with interim Solo AP
firmware, that will join either ZD or SZ controllers. Here is the link for R600 Solo AP (unzip).
https://support.ruckuswireless.com/software/1017-zoneflex-solo-access-point-104-0-0-0-1347-ga-softwa... Take down the ZD1200, and bring up your SZ-100 (make sure it's ready), then HTTP to your
APs, convert the firmware under Maintenance::Upgrade, and reboot. SSH to the AP after it's
on 104.0 code. The Login should be either your ZD admin uid/pw, or 'super/sp-admin'.
Issue a command to tell your AP to look for the SZ-100, 'set scg ip a.b.c.d', then 'reboot'.
It should look for your SZ when it comes back up. Hopefully, you can repeat this for each of
your APs, without needing to factory default them. If factory defaulted, you would need to find
them in your DHCP server lease table, or be directly connected with hard-coded laptop IP.