Updating Linux from an older to newer version

I have some Red Hat Linux 7.2 machines and I would like to update them to
7.3. I know that this can be done with the install program, but is it
technically possible to just manually use rpm to upgrade all of the packages
on a system? Theoretically this might just be "rpm -Fvh *" in a directory
with all of the new packages.

These are pretty Spartan server machines with no gui and a defined list of
packages. And I would like to limit downtime. Is there any merit to
manually updating all packages?

Brian