How do I change how often the Mac App Store in High Sierra checks for updates or notifies me about them?
Yes, you can do this quite easily.
By default the Mac App Store app will check for updates once every week, but you can change this by running a terminal command. Follow these steps:

Launch the Terminal app (by default it's located in the Utilities folder within your Applications folder)

Copy and paste the following command into your Terminal window:
defaults write com.apple.SoftwareUpdate ScheduleFrequency -int 7

The number at the end represents the number of days, so change the ‘7’ at the end to the number of days you’d prefer (i.e. if you change the ‘7’ to ’10’ then it’ll only check for updates every 10 days)

Press Enter


And that’s it! The Mac App Store should now only check for updates as often as you set in the terminal command.