Is there any way to disable APFS local snapshots?
With macOS 10.14, it appears not to be possible to disable local snapshots.

You can remove local snapshots using a method documented in Apple's About Time Machine local snapshots support document:


  How local snapshots use storage space
  
  You don't need to think about how much storage space local snapshots are using, because they don't use space needed for tasks like downloading files, copying files, or installing new software.
  
  Your Mac counts the space used by snapshots as available storage. Even so, Time Machine stores snapshots only on disks that have plenty of free space, and it automatically deletes snapshots as they age or as space is needed for other things.
  
  If you want to delete local snapshots manually, turn off Time Machine temporarily:
  
  
  Open Time Machine preferences from the Time Machine menu  in the menu bar. Or choose Apple menu  > System Preferences, then click Time Machine.
  Deselect "Back Up Automatically" or click the Off/On switch, depending on what you see in Time Machine preferences.
  Wait a few minutes to allow the local snapshots to be deleted. Then turn on Time Machine again. It remembers your backup disks.
  


See also the Apple forum discussion Disable local snapshots in High Sierra with APFS.