Is there any way to select which SSIDs are synched to external APs?

[stego]

you can do this with device tags in InControl2.

Ssid only on one AP

One way to achieve this is Define a tag for the SSID, e.g., “TAG1” Tag the AP(s) that should make that SSID available with the tag (“TAG1”) Define the SSID and set the SSID availability to “SSID available on some devices…”. Then enter the tag (“TAG1”) in the field “Only enable on devices with any of the following tags” That should do it.

Don’t believe you can target individual APs with local AP controller.