Alert when low in IP addresses and make block field optional

We use an internal tool which performs the IP allocation for us. One of the issues there is monitoring the available IP addresses.
It would be good to have email alerting when any of the blocks is running low in IP address.

The reason behind this; as part of the automation, we always use the same parameters hard coded for both space and block (both mandatory). In case the IP address runs out in the respective block, we need to update our automation to use a different block.

Can we make the block field optional so the IP address can be allocated from any of the blocks under the respective block?