Rails: i have a class method and i want to modify something of the instance

something like this:

class Test < Main
   template :box

   def test
      # here I want to access the template name, that is box
   end
end

class Main
   def initialize
   end

   def self.template(name)
      # here I have to save somehow the template name
      # remember is not an instance.
   end
end

that is similar to the model classes:

# in the model
has_many :projects

How do I do it?