so, IIUC, you edited /etc/e-smith/events/actions/nethserver-duc-index
which is an action, not a template
the only way to achieve your needs is to store the --exclude part/list in a db and then use it in the beginning of the action.. you get the values from the db, you create the list using the right syntax and then you use it in the command line..
this is something not trivial
templates are there to templatize the config files.. not the script ones
actions are script and you'd never edit it... first of all because you'll miss your customization every time you update the rpm that owns that file
if you need custom actions to be executed during events, just add your script there, use different names, and link them in the desired event
so, at the end, to solve your issue that script must be modified to accept params from the db..
doing so, you can add as many exclusions you want.. it doesn't matter, 'cause the script will always be executed in the right way