Hi,
You can add more than 20 MACs through CLI:
1. Go to your CLI and log-in.
2. Type vi /etc/config/wireless
3. Press I on your keyboard to start editing the file.
4. Find your access point, it should look something this:
config wifi-iface 'default_radio0'
option device 'radio0'
option network 'lan'
option mode 'ap'
option ssid 'RUT_0F49_2G'
option wifi_id 'wifi0'
option encryption 'psk2+tkip+ccmp'
option key 'j3Z9GbNa'
option macfilter 'allow'
list maclist '00:D8:61:XX:XX:XX'
5. Add more lines like list maclist '00:D8:61:XX:XX:XX' , but use your wanted MAC instead.
6. Exit editing with typing :wq on your keyboard and press Enter to save and quit.
7. Restart wireless service with command /etc/init.d/wireless restart
EB