The video is correct that the patent application can not be changed other than the claims. Thus you need to provide disclosure to support any claims you wish to get. The inclination should be to be more expansive in the description as it may allow for filing continuation applications to get wider patent coverage.
It is possible that the examiner may make you split the patent into two or more patents if they believe that the applications of the invention are different enough. This has happened to me. Either way, you should probably provide enough descriptions of the desired embodiments to support the desired claims. There are strategies to filing patents and I've worked with patent attorneys who have pursued multiple filings for inventions of mine with varied applications.
As I am not a lawyer I wouldn't presume to suggest what you should do. Since you can't describe your invention here anyway, I doubt even a qualified lawyer wouldn't be able to answer such questions. I always suggest working with an actual patent attorney or agent when pursuing a patent. Getting a patent is important, but getting a strong patent is more important. There are programs for obtaining pro bono legal help for patents that you might look into.