Often times I am having to create autoprovisioning templates for each tenant to accommodate things like VLAN settings, custom wallpaper, softkey modifications, timezone, etc. It would be tremendously helpful to be able to make 1 base template for a phone and add in additional 'user defined' variables to the template, similar to ${EXTENSION}, ${SERVER}, ${PASSWORD} etc. These variables could be defined in Thirdlane and added to the template in /etc/asterisk/user_provisioning/, then in the provisioning section in Thirdlane you could open the entry for the MAC address, click 'add variable' like you would add an extension and it would populate that variable in the actual configuration file that is generated.
It would be necessary to establish a default value for the user defined variables and it would be best to have a system level default that can be overwritten by a tenant level default, that would be overwritten by what is defined in the MAC entry in the provisioning section.
The rationale for the multiple default variables is this: A system is deployed and x amount of user variables are defined. Some time later, more user defined variables are needed to be added. For all new tenants, the tenant level default variables will be added when the tenant is cloned/created, but for existing tenants they will need to rely on a system level default variable.