This version number is significant because it represents the baseline installation of .NET 4.0.
No. .NET 4.8 includes all fixes from 4.0, 4.5, 4.6, and 4.7. Installing an old 4.0 hotfix on top of 4.8 is impossible (the installer will block it).
The version number 4.0.30319.1 refers specifically to the initial release of .NET Framework 4.0