Can you add nouns/adjectives/articles in a direct quotation in Chicago MoS keeping the message intact?
You are allowed to add parenthetic words to a quote, so long as your additions are consistent with what the original author was trying to say.  The standard method is to use square parentheses to show an addition or replacement you have made to the quote.  Thus, you can write your altered quote like this:


  "... during an economic downturn, it is no easier to find a job in a region with [a] lower prevailing unemployment [rate] than in one with a higher [prevailing] unemployment rate." 


By putting the additional words in square parentheses you indicate that you have added them to the original quote.  The reader will see that the original author only referred to "unemployment" rather than the "unemployment rate" in the first instance, you have added the additional word.

I tend to agree with other commentators here that this addition is probably unnecessary.  If you particularly want to frame things differently than the quotation, I would recommend paraphrasing here, instead of quotation.  In any case, the above is how you make additions/alterations to a quote if you want to do that.