A server instance represents a particular implementation of a server instance type. The one thing you can change at the server instance level but not the server instance type level is runAssembler arguments.

For example, this code fragment provides different assembly options for the basic_management and management_lock server instances:

<product-addon id="previewOnManagement" >
   <title resource-key="">Configure Preview to run on the CA Server</title>
     <modify-server-instance id="basic_management">
       <add-appassembler-option name="layer" value="preview"/>
     </modify-server-instance>
     <modify-server-instance id="management_lock">
       <add-appassembler-option name="layer" value="preview"/>
     </modify-server-instance>
</product-addon>