I just want to ask if this is possible:
Certain group of APs will advertise a
specific SSID which will not be advertised
by other APs.
This is probably the feature that can help with this requirement;
Have a look at this info;
Enabling WLAN Override
By default, access points transmit all defined WLANs on the controller. However, you can use the WLAN Override option to select which WLANs are transmitted and which ones are not on a per access point basis. For example, you can use WLAN override to control where in the network the guest WLAN is transmitted or you can use it to disable a specific WLAN in a certain area of the network.
From this doc;
Once you create a new WLAN, the WLAN > Edit page for the new WLAN appears. In this page you can define various parameters specific to this WLAN including General Policies, RADIUS Servers, Security Policies, and 802.1x Parameters.
**Check Admin Status under General Policies to enable the WLAN. If you want the AP to broadcast the SSID in its beacon frames, check Broadcast SSID.
Note: You can configure up to sixteen WLANs on the controller. The Cisco WLAN Solution can control up to sixteen WLANs for Lightweight APs. Each WLAN has a separate WLAN ID (1 through 16), a separate WLAN SSID (WLAN name), and can be assigned unique security policies. Lightweight APs broadcast all active Cisco WLAN Solution WLAN SSIDs and enforce the policies that you define for each WLAN.
From this good doc;
Hope this helps!