That code is only run once per application lifetime. Without risking DRY, I don't know what you mean by 'pre-processed'. Do you care if it is run at the parse time instead of the Class Object definition time?
Pre-processed here likely means what you think it means. DRY is not really a concept meant to be applied to method definitions (IMO), but rather method bodies-- of course there are many ways to abuse the interpretation of DRY as well. As far as whether you should care about compile vs load time-- in Ruby you don't need to, but if the language had static typing, it would make a difference.