There might be a way to hijack the splash screen. One of our users always got the same splash screen, instead of the changing series that everyone else got. I always assumed it was some problem with his registry. Try asking in the API forum. The folks who hand out there are more likely to have an answer than us mere mortals. Or maybe try the Administration forum.
I just realized that the splash screen won't work for what you want. Still the folks in the other forums might be able to help.
One way might simply be to make the files read-only in the file system. Then they would get a message from SolidWorks that they were about to modify a read-only file.
A much trickier way would be to embed VBA code in an equation that would run every rebuild. However, it would be complicated to make it run only once per open of the file.