There are no ways to block a device even after multiple connections. However, the time period for which the device waits for the passkey to be entered can be reduced by implementing some application logic. For example , on connection you can store the MAC address of the peer device and compare it on the subsequent connections. If the same devices tries to connect again and again ( update a variable for count) ,after some specific count number, you can send a disconnect command as soon as the same device tries to reconnect.
Note: On connection CYBLE_EVT_GAP_DEVICE_CONNECT event triggers and you can call CyBle_GapDisconnect() API for immediate disconnection and hence you are not waiting for the passkey entry from the same peer device.
Hope it helps.