How to get rid of system is low in storage space notification (MacOS High Sierra 10.13.6)
Since macOS Mojave, you can no longer stop this Agent with launchctl, nor can you edit the plist file. However, you can add an override to prevent it starting by following these steps:


Restart your Mac, and hold down Cmd+R to enter recovery mode
At the recovery mode screen after it loads, select Utilities > Terminal
Execute the command "csrutil disable"
Reboot your Mac, and launch Terminal
Edit the file /var/db/launchd.db/com.apple.launchd/overrides.plist using any text editor (I use vi). You will need to sudo this!
Add the following text

&lt;key&gt;com.apple.diskspaced&lt;/key&gt;
&lt;dict&gt;
        &lt;key&gt;Disabled&lt;/key&gt;
        &lt;true/&gt;
&lt;/dict&gt;

Reboot your Mac again, and once again go into Recovery mode. This time, launch Terminal and enter the command "csrutil enable" before rebooting.


diskspaced will now no longer start, as launchd will see an override that forcibly disables it. Voila.