Updating a file without overriding the list item information

Question

I am working on an app that when a file is created through Office, it asks the user to input the values for the fields that are stored in the Library's List. While that works great, I am completely unable to update that created file without updating its list item information and, while I have tried a huge range of options, it always override everything. I cannot ask the user to re-enter those values and the file might be in-memory or downloaded from SharePoint Online directly.

I only want to update the file's content, and I can use a byte[] or a Stream as needed. I am using this right now, just to try stuff out:

using (var context = new ClientContext(repositoryUri + "subSiteName"))
{
    context.Credentials = CurrentUser.Credentials;

    var web = context.Web;
    try
    {
        context.Load(web.Lists, all => all.Where(l => l.RootFolder.Name == "libraryName").Include(l => l.RootFolder));
        context.ExecuteQuery();
        var list = web.Lists.FirstOrDefault();

        var folder = list.RootFolder;

        context.Load(folder, f => f.Files);
        context.ExecuteQuery();

        var file = folder.Files.Where(f => f.Name == "fileName" /* hard-coded for testing */).FirstOrDefault();

        var fileInformation = new FileCreationInformation
        {
            Content = fileData,
            Url = file.ServerRelativeUrl,
            Overwrite = true // false: throws, true: overwrites list item
        };

        var newFile = folder.Files.Add(fileInformation);

        context.ExecuteQuery();
    }
    catch (Exception ex) // just to read exception messages
    {

    }
}

Is there a way to just update the binary? I use the REST API but now switched to CSOM to see if there was any better option.

Answer 1

I found an unwanted answer that at least works. After observing that SharePoint keeps metadata on Office files after it downloads them, I decided to do the same.
Now, when the file is saved as "new" by the user, I:

1. Upload it, and keep its new URL
2. Update its metadata using the file's URL
3. Download the file to a temporary location
4. Open that file without the user knowing about it.

The result is that when the file is saved again, the metadata is kept.