Ah. That would have been a good solution.
I didn't get that until I had tried to change the SSIDs from the old to the new.
I am using the Shelly Smart Control app. It doesn't seem to have the WiFi Batch Change option so I did the following:
Reverted to the old router and WiFi
Connected to each of the two Shelly PM1 plus devices and changed the SSID for each to the new SSID and password. and Enabled the change.
Then changed to the new router and WiFi.
Shelly Smart Control now saying "Device Offline" for each device. So - cant access them.
Reverted again to the old router and WiFi and now (because I changed the SSID?) Shelly Smart Control now says "Device Offline" for each device.
Help!
I now seem to have no way of getting access to either of the devices. I'm at my wit's end.
I have gone through the motions of resetting one of the devices (switching on and off 5 times) and I think it has reset because it's signal no longer shows up on a WiFi signal analyser-while the second device still does.
Later ....
I found that Shelly WiFi signal on my phone (in the available WiFi list).
I connected to it and (through its own web page) set the SSID to the new network name and clicked "Enable".
Reconnecting my phone to the new network again I opened Shelly Smart Control app .
The reconfigured Shelly is still showing as Offline.
I hope someone can suggest something for me.