Store all common items in a template ‘Template SNMP’.
The attribute ‘SNMP community’ is set to the user macro ‘{$SNMP_COMMUNITY}’ in all these items.
Add a user macro {$SNMP_COMMUNITY} = public to the ‘Template SNMP’

Then create one template per customer (e.g. ‘Template SNMP – ACME’) and link it to the common template ‘Template SNMP’.
Add a user macro ‘{$SNMP_COMMUNITY}’ to the customer template as well. But this time with the individual community string.