Can I add mint flavoring to ready made royal icing? I have a 250g block of black Regalice from Redshaws. I want to flavor the icing with a concentrated peppermint flavoring. Only a very small amount to achieve a subtle hint of mint, the icing is just to lay over the cake.. Will the icing become to moist/tacky if I add any kind of liquid? I plan to use edible silver paint to add some details when it is finished. 

If it does become too moist, what can I do to help it become dry?

I do not want to mess up and I am on a deadline so please help me :)

Thank you!
Yes you can in small quantities. My mum used to do a lot of cake decorating, and still does bits with my kids.
Adding small amounts of liquid such as flavoring/colouring is perfectly fine. It is important to knead it in properly. You can use a small quantity of icing sugar to prevent it sticking, but the main thing is to keep handling to a minimum where possible as the heat in your hands is more likely to make it sticky.

In terms of application, we typically use wooden tooth picks and dot the flavoring/coloring in, then repeat as necessary.