I think it is a bad idea personally. In order to do this you will need to boil said coriander and orange peel in some water and then cool and then add it to the finished beer. I think you are better off sticking with your finished product, enjoying it, and then doing this to your next batch. With your next batch you would add these with 10 min’s left in the boil. Adding these things will by no means ruin your batch as long as you sanitize them by boiling, but if the finished product is at all drinkable then leave it as is, and expirement on the next batch. Just my opinion of course.
Or, you could try soaking them in vodka for a few days then add the whole thing to the secondary. The vodka should take care of any nasties in the coriander or orange peel. Just my opinion.