It happens quite often that we retrieve SNMP data that contains IP addresses which we then use in the name of a trigger of item that's created in the discovery rule.

BGP, OAM, and other such sessions are examples of this.

It would be great if we could use the hostname instead of the IP address in the item or trigger name, or even in tags and such.

A macro function as described here would probably work well:

https://www.zabbix.com/documentation/current/en/manual/config/macros/macro_functions#supported-macro-functions