I have 7 individual displays that until now have all been playing the same content. I have been using one layout for all 7 screens since the content was all the same. I now need to add a new file to the content loop but only to 2 of the 7 screens. Is there a way to add the new media file to the display directly so it will continue to play the assigned layout plus the new file, or do I need create a new layout for the 2 displays? Please help!
Campaigns
Create a new layout with the new media file on it. Then create a campaign, add both the layouts to the campaign. Changed the default layout on each screen to a simple layout that only has 1 media image on it. (This is in case things stop playing it will show that file, over and over) Now schedule the layout that contains the original media to the screens that do not need the new media on it. Then schedule the campaign to the two screens you need the new media on. Make sure the schedules are set to either repeat, or the end date is far in the future, like say the end of next year.
I hope that is clear enough. If not, let me know 
I think Im following you. One question though…can you assign multiple layouts to a Display or is that the purpose of setting up a campaign?
Yes, that is what campaigned are best at. You can also just use the scheduler to set multiple layouts at different times.