In CA Spectrum 10.2 and above, a new attribute was added to the WLC Application model that controls the AP discovery. The attribute is named enableAPDisc. Setting the value to False will disable the automatic AP discovery. Setting it back to true will trigger the discovery. As noted, the attribute is available on the WLC application model:
There are different ways to find the application model, but here is one suggestion.
In the CA Spectrum OneClick Locater view, create a new search for "ModelTypeName" "Equal to" "Cisco_LWAPP_App" or "Aruba_Controller_App".
The resulting list will contain the WLC application models. Find the model(s) you wish to disable the AP discovery on and change the enableAPDisc (0x13340) from True to False.