If a file listed on the Design panel is changed outside of the view of BSS, the changes are not reflected in the design. That's to be expected -- watching the list and automatically re-importing a file would slow down BSS. It would also be "dangerous" since a change to a file may not necessarily indicate that it is ready for inclusion.
Currently to bring a fresh copy of a file into the design, you must: (1) delete the current copy; (2) import a new copy; (3) adjust the "Include Order" (particularly for JS files). Three steps -- Yucch!
I suggest that a new "Reimport" action be added to the menu that pops up in response to a right mouse click on a filename. "Reimport" should replace the design's current edition of the file and -- importantly -- maintain the file's position in the "Include Order". One step -- Yea!
Other than the order, pretty much the same thing that is done with the images. You can import images and if it detects the same file name it asks if you want to overwrite/replace the old one. Should be able to do that with all files so I would have to agree here! Plus, I would think if it's set to replace it, it would automatically (for us anyways) set the include order as the same as the old file.
I thought I had a workaround by using "Link External JS" but something (Chrome? the preview server?) wouldn't accept a file:/// URI. ... Oh, well ...
But it should be a single click "Reimport" action by the user instead of 2 clicks (Import and then Confirm).
It shouldn't accept anything that starts with file:/// actually, as that's all local to you and not to an uploaded site. You would need to upload whatever it is you want to create a CDN for and link it that way. Haven't tried it myself so I'm not sure if there's anything special you need to do to create a CDN, but I do know it needs to be an external URL rather than an internal one. :)
It was worth a shot ... I've already set up a dedicated server on my development machine to dish out JSON and was trying to avoid setting up yet another server to act as a CDN. There's no uploading involved ... all the files are still here on my development machine and haven't been uploaded to a "far away" server yet.
Maybe I can use XAMPP to serve my files to myself ... but that's for another day.
Another more easily setup option is to set the files up the same as they will be on the server. This way you can use "relative" links instead of absolute and it won't matter where the files are then. Unfortuntately I don't think you can do that with CDN's, but you should be able to do it with everything else. My suggestion would be this:
Upload your file that you need the CDN for to where it will reside when the site is complete. Create your CDN using a full link, which is more appropriate for CDN's anyways really. Do all the rest with relative links and then it won't matter where you have your site testing, be it locally or uploaded it will always work.