As you mentioned that you added an entry to "DEFAULT_AP_LIST" in "dct.c" and defined an AP in "wifi_config_dct.h" but it gives error unless you define the same in "default_wifi_config_dct.h". This might be because you have to define the which wifi_config file to use in the .mk file of the application.
To make you application use the "wifi_config_dct.h" add this to the .mk file
WIFI_CONFIG_DCT_H := wifi_config_dct.h
This will make sure it uses the wifi_config_dct.h of the application not the "default_wifi_config_dct.h".
I hope this helps.