Any attribute that can hold multiple values, is replaced on mass-updates.
- Applications on items
- Flexible intervals on items
- Host groups on hosts
It seems fine for "Link additional templates" on hosts.
The GUI seems to offer no possibility to do the following mass-update:
Item A, Application A
Item B, Application B
Item A, Application A, Application Z
Item B, Application B, Application Z
I haven't found out, if it's possible with the API. I don't dare to do it in the database because of the code sitting in the frontend, that handles template inheritance.
Might be related to https://support.zabbix.com/browse/ZBXNEXT-170