you can use instance filter script to modify instance itself or just instance name. For example, if you instance is two numbers connected with dot you can use the following filter script:

instance = $1;
if ($1 ~= "[0-9]+\\.([0-9]+)")
{
   return %(true, instance, $1);
}
return true;

This script will keep instance as is (i.e. 4.2) but set instance name to second number (i.e. 2). You can then use {instance-name} in description to insert updated display name.

Best regards,
Victor