Metadata is the term you are looking for. (Doing a Google search for adding metadata in an mp4 will likely provide fruitful results.)
Since you shouldn't be using After Effects to make an MP4 at all, this is probably a question better-suited to the Adobe Media Encoder forum.
There's a button right at the bottom of the Export Settings window in the Adobe media encoder. There is also a Metadata panel in After Effects. You'll find it under the Window Menu. Window>Metadata. If you add Metadata to your projects any renders that support Metadata will have it included when you render in the AME. In the AME you can check the metadata and edit it. The Render Cue does not include XMP metadata in rendered files by default If you want the data you created for the Project in the Metadata Panel you'll need to enable the checkbox in the Output Module settings.
All of this is covered in the AE help files and can be found by typing metadata or exporting or rendering in the Search Help field at the top right corner of AE.
Thanks for your responses. Metadata was the term I was looking for. Kind of hard to search for a solution when you don't know what you're looking for.
Rick, adding Metadata on all AME renders through Windows > Metadata is a great tip.
I was specifically asking about making the metadata unchangeable so no one can simply Right-click the .mp4 file > Properties and change the author information.
I believe I overthought the problem because all I had to do was make it a Read-only file type in the .mp4 Properties.
If you set up your metadata in AE or in Premiere Pro it will stick to everything you do and you'll only have to enter it once for every project. If you use the AME you have to add it every time you render for every file.