You are welcome to check how UNA is documented by checking this documentation which is generated from source code and updated every day:

https://ci.una.io/docs/

To change something in the core we have 'alerts' which are actually 'hooks' which can be used to change different things in the core. But this hooks aren't available everywhere, but you are welcome to ask us to add hooks where you need and we'll do it in the next update.

Also we are going to add circles (privacy groups) in UNA 10 - https://github.com/unaio/una/issues/1909