https://www.zabbix.com/documentation/devel/en/manual/config/items/preprocessing#snmpwalk and all other versions.

Unchanged - return hex-string as unescaped hex string

Hex values can have displayhints. Presumably the current "unchanged" only affects custom processing by Zabbix - it does not affect applying displayhints.

It would be great to explain here (or link from here) that "changing" could happen either from displayhints or by Zabbix on its own, and what exactly "unchanged" does.