If your runtime license is visible to the FTAM software, it will limit you when editing. I had a similar issue when I imported a RSView32 project I thought had only about 7 displays plus one or two pop-ups.
I ordered FT Studio and a runtime license for 25 displays. After finagling the import process and getting it all set up and imported, I discovered the same issue you had. I could not even look at it. So, I contacted our automation support specialist and he suggested "hiding" the runtime license file. Since both the studio license and the runtime license were in the same text file, I made a copy first and just stuck it in the "My Documents" folder, then edited original license txt file (in the FTAM license search path) removing the portion related to the runtime license.
Afterward I was able to open, backup and edit the application. I could even run the application. I believe that the studio license includes runtime capability with some time limitations, but don't hold me to that. The original project, it turned out, actually had 37 display pages but most of them were left overs or otherwise abandoned. I did not want to buy RSView32 Works just to perform the import, and did not know enough about RSView32 to be able to properly count them in the original project format.
Once I had the new stuff added and everything whittled down to the required 23 displays, with FTView shut down, I deleted my edited license file and moved the original one back to the license folder in the FTAM path and all works as it should.