I would like to update our remote systems from CentOS 7.2 to 7.3. Is there an option that would only install the minimum number of packages required? The standard upgrade would involve downloading almost 800MB of packages.
No. Not really.
If you're running the upgrade, that means new GLIBC and kernel and supporting packages will be downloaded and installed. In addition, any updates to the packages already present on the system will be downloaded.
This seems like an X-Y problem question. Why is downloading 800mb of packages a problem?
Look at the list of packages it wants to update. Remove any that you don't use and aren't dependencies of something you do use. Retry until satisfied with the download size, then deploy the resulting package removal command to the rest of your servers before upgrading them.
Use that same list to build future servers. No point installing software packages you aren't going to use hundreds of times over, much less keeping them all upgraded.
If nothing needs to be removed, then that 800 MB upgrade is your minimal upgrade.