It could be great for actions to have implemented possibility not just to fill separate notification message subject and body, but also to be able to have defined something like "notification message templates" (for inspiration, Jira itself has similar concept implemented for its notifications), defining subject+body templates, reusable (referenced) in more than 1 action.
Disadvantages of current state: when you have e.g. 100 actions, you need to have also subject and body copypasted 100 times, when you want to have unified form of notification messages. Then, when you want to change form of unified message, you need to edit 100 actions (burdening, error-prone process, hardly-maintainable). Complexity increases, when you have several types of messages (subject+body), each defined in many various actions, in the same ZABBIX system.
Advantages of suggested feature: definig just one "notification message template" for each notification message type, and assigning them (optionally?) to actions as default, recovery, and acknowledgement messages in actions' operations.
Thank you in advance for consideration, and sorry for my rude "Major" priority classification and "4.0 (plan)" suggested fix version, but I feel it this way .