I have a requirement whereby the default image for an image field in the article node should be set for a 6 month period of time and then the default image changes for the next 6 months and so on. I tested this in the article content-type by setting the default image and then creating content off the content-type. I then changed the default image and created new content. This changed the images in the new and old contents. I would like the old content to retain the old default image and the new content to reflect the new default image. Any pointers on how to do this?