Is it possible to add dynamically (on run-time) values to android resources file? For example to add new string to string.xml or to add new item to existing string array.
No, it is not possible to add values dynamically to any part of your resources.
All resources are compiled into a read-only binary file when you generate your apk, and you cannot add extra data to it. You will have to use the internal or external storage for such data.